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Worcester Bosch Boiler Fault Codes

Worcester Bosch Group

In the unfortunate event that your Worcester Bosch boiler develops an issue, it will enter a locking or blocking condition, and fault code information will be presented on the boiler display. So that you can quickly identify what the fault code means and what should be your next course of action, we have developed the below fault code finders for the Worcester Bosch range. Just click on your boiler from the below list and then search for the fault code that your boiler is displaying or view fault codes that aren’t displayed. The fault code finder will then provide you with a diagnosis, which will assist you should you need to contact an engineer.

Worcester Bosch Greenstar 2000 Gas Boiler Fault Codes

Worcester Bosch Greenstar Si Compact Gas Boiler Fault Codes

Worcester Bosch Greenstar i Gas System Boiler Fault Codes

Worcester Bosch Greenstar 8000 Gas Boiler Fault Codes

Worcester Bosch Greenstar CDi Compact Gas Boiler Fault Codes

Worcester Bosch Greenstar CDi Highflow Gas Boiler Fault Codes

Worcester Bosch Greenstar 8000 Style Gas Boiler Fault Codes

Worcester Bosch Greenstar Heatslave II Oil Boiler Fault Codes

Worcester Bosch Greenstar 24/28/30 Gas Combi Boiler Fault Codes

Worcester Bosch Greenstar 2000 Gas Boiler Fault Codes

Fault Codes
Pump Operation and Diagnosis
Faults that are not Displayed

Fault Codes

Fault codeFault categoryDescriptionRemedy
200OThe device is in central heating mode.–
201OThe appliance is in DHW mode.–
202OThe appliance is in optimised switching mode: the interval for restarting the burner has not yet
expired ( service function 3-b2).
–
203OThe appliance is on standby, there is no heat
demand.
–
204OThe current flow temperature is higher than the set flow temperature. The burner has been
switched off.
–
207–Operating pressure too low.▶ Fill and vent the system, check the system for leaks.
▶ Replace pressure sensor if necessary.
208OThe appliance is in chimney sweep mode. Chimney sweep mode is deactivated
automatically after 30 minutes.
–
212–Temperature increase for safety or flow
temperature sensor too fast.
▶ Open the shut-off valves.
214VThe fan stops during the safety time.▶ Check fan, replace if necessary.
▶ Check mains voltage.
215VFan too fast.▶ Replace fan.
▶ Mains voltage must correspond to the default value.
▶ Check PCB and fan harness, replace if necessary.
224
224
B VFlue gas temperature limiter or heat exchanger temperature limiter has tripped.If the blocking fault persists for a prolonged period, it becomes a locking fault.
▶ Check position of isolation valve in heating circuit, open if required.
▶ Check water pressure, if necessary top up until the preset pressure is reached.
▶ Check the temperature limiter and connecting lead of the heat exchanger for breaks, replace if required.
▶ Check the flue gas temperature limiter and the connecting lead for breaks, replace if required.
▶ Vent appliance with service function 4-A1 ( page 45).
227
227
B VNo flame detected.After the 5th ignition attempt, the blocking fault becomes a locking fault.
▶ Check whether the gas isolator is open.
▶ Check the gas supply pressure.
▶ Check ionisation signal.
▶ Check the power supply.
▶ Check the electrodes with cable, replace if required.
▶ Check the flue system, clean or repair if required.
▶ Check gas/air ratio, adjust if necessary.
▶ Clean heat exchanger.
▶ Check the gas valve, replace if required.
▶ Check burner setting, correct if necessary.
228VFlame signal is present although burner is switched off.▶ Check if there is a flame present.
▶ Check electrodes and connecting leads, replace if required.
▶ Check the gas valve, replace if required.
▶ Check appliance electronics, replace if necessary.
229BFlame lost during burner operation.▶ Check the main shut-off valve, open if necessary.
▶ Check the appliance isolation valve, open if necessary.
▶ Measure the gas supply pressure at the rated heat input. If necessary, shut down the appliance and check the gas line.
▶ Check flame sense electrode and connecting lead, replace if required.
▶ Check venturi/injector for potential blockage.
▶ Measure the ionisation current.
▶ Check the protective conductor connection in the control unit.
▶ Check the ignition cable for damage, replace if necessary.
▶ Check functionality of gas valve and replace if necessary.
▶ Check burner setting value at rated heat input.
▶ Check burner setting value at the lowest output.
▶ Check flue system.
▶ Check combustion air supply.
▶ Check the heat exchanger on the flue gas side for deposits, clean if necessary.
232BHeat source locked by external switching contact.▶ Connect the plug for the external switching contact.
▶ Install jumper/check condensate pump according to manufacturer's specifications.
▶ Adapt switching point of the external temperature switch to the system.
▶ Replace connecting lead to the external temperature switch.
▶ Replace external temperature switch.
233VFault in code plug or appliance electronics.▶ Check whether code plug is installed.
▶ Check appliance electronics, replace if necessary.
234VElectrical fault in gas valve.▶ Check the connecting lead, replace if required.
▶ Check the gas valve, replace if required.
235VVersion conflict between appliance electronics and code plug.▶ Check software version of appliance electronics and code plug.
▶ Replace appliance electronics or code plug.
237VSystem fault.▶ Check and replace code plug.
▶ Check and replace the appliance electronics.
238Vappliance electronics faulty.▶ Check and replace the appliance electronics.
242VSystem fault, appliance electronics.▶ Reset control appliance / burner control unit - factory reset.
▶ Reconnect electrical connections at control unit / burner control unit correctly.
▶ Replace the control unit/burner control unit.
244VSystem fault, appliance electronics / basic controller.▶ Reset control unit / burner control unit - factory reset.
▶ Reconnect electrical connections at control unit / burner control unit correctly.
▶ Replace the control unit/burner control unit.
246
247
257
–Internal burner control fault.▶ Reset burner control - factory reset.
▶ Check electrical connections of burner control.
▶ Replace burner control.
245
249
250
251
252
253
254
V V V V V V
V
System fault, appliance electronics.▶ Reset appliance electronics - factory reset.
▶ Check electrical connections.
▶ Replace the appliance electronics.
256VSystem fault, appliance electronics / basic controller.▶ Reset control unit / burner control unit - factory reset.
▶ Reconnect electrical connections at control unit / burner control unit correctly.
▶ Replace the control unit/burner control unit.
258VInternal fault in control unit.▶ Reset control unit - factory reset.
▶ Reconnect electrical connections at control unit correctly.
▶ Replace control unit.
259
262
263
V V VSystem fault, appliance electronics.▶ Reset appliance electronics - factory reset.
▶ Check electrical connections.
▶ Replace the appliance electronics.
264BAir feed failed during operating phase.▶ Reconnect the fan plug properly, perform reset.
▶ Replace fan.
▶ Mains voltage must correspond to the default value.
▶ Remove any blockages in the flue system.
▶ Check venturi/injector for potential blockage.
265BCHeat energy demand lower than energy
supplied.
–
268–Component test mode.Not applicable, is status message.
269VFlame monitoring.▶ Reset appliance electronics - factory reset.
▶ Replace the appliance electronics.
▶ Check flame sense electrodes and connections.
▶ Check earth connections.
270BCThe heat source has started up.–
273OOperation interrupted: safety inspection
following 24 hours of continuous operation.
–
275OTest code plug detected.–
281–Pump stuck or running dry.▶ Replace the pump.
▶ Vent the system.
▶ Check operating pressure.
▶ Check low pressure switch.
▶ Check pump connections (hydraulic and electrical).
305BCBoiler cannot start temporarily following DHW
priority.
System appliance only.
306VAfter switching gas off: Flame is detected.▶ Check the gas valve, replace if required.
▶ Check electrodes and connecting leads, replace if required.
▶ Replace the appliance electronics.
323–Control communication fault.–
328VMains voltage briefly interrupted.▶ Check for voltage interruption between electrical wiring system of the building and
the appliance.
341BHeat source temperature increase too rapid.▶ Open isolation valves.
▶ Connect plug to pump.
▶ Replace pump.
▶ Ensure circulating pump is set on Constant speed mode - curve III.
342BCTemperature increase in DHW mode too rapid.▶ If the water pressure is too low, top up with water and vent the system.
▶ Open service valves in the cylinder charging circuit.
▶ Replace the diverter valve / cylinder primary pump.
350BFlow temperature sensor short circuit.bookmark0
351BFlow temperature sensor failure.bookmark0
356BSupply voltage for heat source too low.▶ Establish supply voltage of at least 196 VAC.
357BCVenting program–
358BCActive anti-seizing function.Blocking protection for the heating pump and diverter valve active
360VIncorrect code plug.▶ Check code plug, replace if necessary.
362VService code plug detected.▶ Check code plug, replace if necessary.
363VSystem fault, appliance electronics: fault when testing the ionisation signal.▶ Check earthing connections.
▶ Reset appliance electronics, replace if necessary.
364VSolenoid valve EV2 leaking.▶ Check the gas valve, replace if required.
▶ Check electrodes and connecting leads, replace if required.
▶ Check and replace the appliance electronics.
365VSolenoid valve EV1 leaking.▶ Check the gas valve, replace if required.
▶ Check electrodes and connecting leads, replace if required.
▶ Check and replace the appliance electronics.
604VSystem fault, burner control unit.▶ Reset appliance - factory reset.
▶ If the fault persists following a reset, the burner control unit is faulty and must be
replaced.
810–DHW temperature has not increased for 2 hours.▶ Prevent water from escaping.
▶ Position DHW temperature sensor correctly.
▶ If no voltage can be measured, then the MC10 control panel is faulty and must be replaced.
▶ If power is being supplied to the DHW cylinder charge pump but it is still not running, it is faulty and must be replaced.
▶ If power cannot be supplied to the DHW cylinder charge pump, then there is a problem in the cable between the control panel and pump. Check screw terminals and cables.
▶ If current is not being supplied to the 3-way valve, there is a problem in the cable between the control panel and valve. Check screw terminals and cables.
▶ If current is being supplied to the 3-way valve but it is still not working, the valve is faulty and must be replaced.
▶ If a voltage of approx. 230 V is measured at the terminals and the pump is not running, the pump is faulty and must be replaced.
▶ Eliminate all faults in the cables. Vent if necessary.
▶ Replace the pump if there are any deviations whatsoever.
▶ Set the DHW heating to “Priority”.
▶ If readings are different to the values in the table, replace the sensor.
815RFaulty low loss header temperature sensor.▶ Check the sensor port.
▶ Check the temperature sensor for incorrect installation position or breakage.
1013RMaximum combustion point reached.▶ Check plausibility of displayed cylinder temperature.
▶ Check plug-in connectors and cable harness for contact.
▶ Replace cylinder temperature sensor.
1014–Ionisation current is too low.–
1017RWater pressure too low.▶ Check water pressure, if necessary top up until the preset pressure is reached.
▶ Check pressure sensor, replace if required.
1018WService time expired.▶ Carry out maintenance.
1021RDHW temperature sensor faulty.bookmark1
1022–DHW temperature sensor is faulty.–
1023RMaximum operation time including standby is
reached.
▶ Perform inspection.
1065RPressure sensor faulty or not connected.▶ Check plug, connect correctly.
▶ Check pressure sensor, replace if required.
▶ Check connecting lead for breaks or short circuits, replace if required.
▶ Check and replace the appliance electronics.
1068ROutside temperature sensor faulty.▶ Remedy contact problem.
▶ Replace the sensor.
1073RFlow temperature sensor short circuit.▶ Check flow temperature sensor, replace if necessary.
▶ Check connecting lead for short circuits, replace if required.
▶ Check and replace the appliance electronics.
1074RNo signal from the flow temperature sensor.▶ Check plug, connect correctly.
▶ Check flow temperature sensor, replace if necessary.
▶ Check connecting lead for breaks, replace if required.
▶ Check and replace the appliance electronics.
1075RShort circuit in heat exchanger temperature limiter.▶ Check heat exchanger temperature limiter, replace if required.
▶ Check connecting lead for short circuits, replace if required.
▶ Check and replace the appliance electronics.
1076RNo signal from heat exchanger temperature limiter.▶ Check plug, connect correctly.
▶ Check heat exchanger temperature limiter, replace if required.
▶ Check connecting lead for breaks, replace if required.
▶ Check and replace the appliance electronics.
2051–Internal fault.▶ Disconnect power from the system for 30 seconds.
▶ Check and replace control unit.
▶ Notify customer service.
2085
2908
V VInternal fault in burner control unit.▶ Reset appliance.
▶ If the fault persists following a reset, the burner control unit is faulty and must be replaced.
2909–System fault, appliance electronics / basic
controller
▶ If the fault persists following a reset, the burner control unit or Key (including
interconnecting leads) is faulty and must be replaced.
2910VFault in flue system.▶ Check whether a flue system is connected, install if required.
▶ Check for unobstructed cross-section of flue system, remove deposits if required.
2911–Calibration failed.▶ Replace faulty component.
2912–No flame signal during calibration.▶ Replace faulty component.
2913–Flame signal too low during calibration.▶ Check and replace flame sense electrodes (and interconnecting leads).
2914–System fault, appliance electronics.▶ If the fault persists following a reset, the appliance control unit is faulty and must
be replaced.
2915VSystem fault, appliance electronics.▶ Reset appliance.
▶ If the fault persists following a reset, the control unit is faulty and must be replaced.
2916VSystem fault, appliance electronics.▶ Reset appliance.
▶ Trigger heat demand.
▶ End heat demand.
If the fault persists, the control unit is defective and must be replaced.
2917VNo flame signal when checking the combustion control.▶ Disconnect power and then reconnect.
▶ Trigger heat demand.
▶ Wait 5 minutes.
▶ If the fault re-occurs within that time, reset the appliance without disconnecting the supply voltage.
This triggers a calibration of the ionisation circuits.
▶ If the fault is still present after the calibration, the control unit is faulty and must be replaced.
2918–Fault in the flue.▶ Clean the siphon and drain water out of the appliance (gas side).
2920VFlame monitoring fault.▶ Check electrodes and connecting leads, replace if required.
▶ Check earthing connections.
▶ Check appliance electronics, replace if necessary.
2921BThe appliance is in test mode ( Menu 5,
page 46).
–
2922–Internal burner control fault.▶ Check and replace control unit.
2923
2924
V VSystem fault, appliance electronics.▶ Reset appliance - factory reset.
▶ If the fault persists following a reset, the appliance electronics are faulty and must
be replaced.
2925
2926
V VSystem fault, appliance electronics.▶ Check the gas valve, replace if required.
▶ Check appliance electronics, replace if necessary.
2927BNo flame detected during ignition.▶ Check the main shut-off valve, open if necessary.
▶ Check the appliance isolation valve, open if necessary.
▶ Measure the gas supply pressure at the rated heat input. If necessary, shut down the appliance and check the gas line.
▶ Check flame sense electrode and connecting lead, replace if required.
▶ Check venturi/injector for potential blockage.
▶ Measure the ionisation current.
▶ Check the protective conductor connection in the control unit.
▶ Check the ignition cable for damage, replace if necessary.
▶ Check functionality of gas valve and replace if necessary.
▶ Check burner setting value at rated heat input.
▶ Check burner setting value at the lowest output.
▶ Check flue system.
▶ Check combustion air supply.
▶ Check the heat exchanger on the flue gas side for deposits, clean if necessary.
2932–Internal fault.▶ Restart the appliance.
2928
2930
2931
2940
V V V
V
Internal fault in burner control unit.▶ Reset appliance - factory reset.
▶ If the fault persists following a reset, the burner control unit is faulty and must be replaced.
2941BInsufficient flow rate in heat source.▶ Check plug of flow temperature sensor, connect correctly if required.
▶ Check flow temperature sensor, replace if necessary.
▶ Check pump for blockage, clear if required.
▶ Check pump settings, correct if required.
▶ Check water pressure, if necessary top up until the preset pressure is reached.
2942–No fan speed feedback.▶ Connect plug for speed control to the fan.
▶ Connect plug for power supply to the fan.
▶ Check fan harness.
▶ Check and replace control unit.
2943–Mains voltage too low.▶ Establish supply voltage of at least 196 VAC.
2945VToo many short heat demands in a short time.▶ Reset appliance - factory reset.
▶ Increase restart blocking time.
▶ Make sure that at least one thermostatic valve is open.
▶ Check and replace faulty heating pump.
▶ Check diverter valve functionality, replace if necessary.
2946VIncorrect code plug.▶ Check code plug, replace if necessary.
2947RAnti-seizing function is activated.The function stops automatically.
2948BNo flame signal with low output.The burner restarts automatically after purging.
▶ Check CO2 settings.
2949BNo flame signal with high output.The burner restarts automatically after purging.
▶ Check burner gaskets, replace if required.
▶ Check CO2 settings.
2950BNo flame signal following starting procedure.▶ Check CO2 settings, adjust if necessary.
▶ Check Burner and heat exchanger gaskets
▶ Check gas pressure during burning at full load
▶ Burner restarts automatically after purging
2951VLoss of flame too frequent.▶ Refer to the blocking error(s) that lead to this locking error. Check the fault history on appliance.
▶ Possible purging of gas pipe incomplete.
▶ Could also indicate a wide variety of issues such as pipework undersized or gas pressure dropping off, incorrectly routed condense drains, incorrectly sited flues,
incorrectly wired etc.
2952VInternal fault when testing the ionisation signal.▶ Restart appliance to see if problem re-occurs.
▶ If the fault remains after resetting, the burner controller (PCB) is defective
2953BNo flame signal with low output.The burner starts automatically after cleaning (purge).Possible cause high winds.
▶ If the fault occurs repeatedly, check the settings of the CO2 values.
▶ Check Flue integrity.
▶ Check flue terminal.
2954BNo flame signal with high output.Burner restarts automatically after purging.
▶ Check and replace burner gaskets.
▶ Reduce burner load.
▶ If the fault occurs repeatedly, check the settings of the CO2 values.
▶ Check Flue integrity.
▶ Check flue terminal.
2955BThe heat source does not support the specified parameters for the hydraulic configuration.▶ Check hydraulic configuration, correct if necessary.
▶ Check menu L2, default setting 0 required.
2956OHydraulic configuration at the heat source is
activated.
–
2957
2958
V VSystem fault, appliance electronics.▶ Reset appliance electronics.
▶ Check electrical connections.
▶ Check and replace the control unit.
2959
2960
B
B
System fault, appliance electronics.▶ Check and replace the control unit and code plug.
2961
2962
V VNo signal from fan.▶ Check mains voltage to fan.
▶ Check fan harness for continuity, replace if required.
▶ Check the Pulse width modulation (PWM).
▶ Check and replace the fan.
▶ Check and replace the PCB.
2963RThe signal from the heat exchanger temperature limiter and flow temperature sensor is outside the permissible range.▶ Check flow through appliance and system is filled.
▶ Check for air locks in the system. Purge if required.
▶ Check Heat exchanger sensor (primary thermistor) and plug connected to stat.
▶ Check resistance of stat. Replace if required.
▶ Check continuity of harness. Replace if required.
2964BInsufficient flow rate in heat exchanger.▶ Supply sensor is not assembled on the supply pipe.
▶ Supply sensor does not make proper contact to the supply pipe.
▶ System is not filled with water.
▶ No water flow, because CH system is closed.
▶ No water flow, because pump is not operating correctly.
2965BFlow temperature too high.▶ Check flow through appliance and system pressure.
▶ Check for air locks in the system. Purge if required.
▶ Check isolation valves.
2966BFlow temperature increase in heat exchanger too rapid.▶ Check flow through appliance and system pressure.
▶ Check for air locks in the system. Purge if required.
▶ Check isolation valves.
▶ Check pump is operating freely, check voltage to pump
2967BTemperature differential between flow temperature sensor and heat exchanger temperature limiter is too great.▶ Check flow through appliance and system filled.
▶ Check for air locks in the system. Purge if required.
▶ Check isolation valves.
▶ Check pump is operating, check voltage to pump.
▶ Check heat exchanger sensor and flow sensor are making contact with the pipe work.
▶ Check heat exchanger sensor and resistance of stat. replace if required.
▶ Check continuity of harness. Replace if required.
2968–Refilling of system in progress.Not applicable in the UK/IE
2969–Maximum number of refills reached.Not applicable in the UK/IE
2971VOperating pressure too low.▶ Vent the heating system.
▶ Check water pressure, if necessary top up the system pressure.
▶ Check pressure sensor, replace if required.
2972VMains voltage too low.▶ Check mains supply voltage on appliance L and N connections.
2973–System fault, appliance electronics / basic controller▶ Perform reset - factory reset.
▶ Check and replace control unit.
2974–Internal error▶ Restart the appliance and check if fault remains.
▶ Check and replace control unit.

Pump Operation and Diagnosis

LED colour DescriptionDiagnostic Potential causeRemedy
Green -
continuous
Normal operationPump runs as expectedNormal operation--
Green/Red - blinkingWarning mode (pump operating in an abnormal condition, no risk for the pump functionality).The pump is running but sent a warning message.• Dry run:
– The pump is operating without water.
▶ Check appliance system pressure and top up as required.
• Overload of motor:
– Friction due to particles and
/or impeller blocked with debris and /or too high
viscosity.
▶ Check installation water quality, clean system if debris is present.
• Generator operation:
– The pump rotor is driven by an external flow.
▶ The pump will operate normally when the external flow will be stopped.
Red - blinkingAbnormal running mode (pump stopped but still functioning).The pump has stopped due to external failure.
The pump will restart itself after the disappearance of the external failure.
• Under or Over voltage:
– Mains supply voltage
U<160V or U>280V.
▶ Check mains voltage supply to pump: 160V < U < 280V.
• Overload of motor:
– Friction due to particles and/ or impeller blocked with debris and/or too high
viscosity.
▶ Check installation water quality, clean system if debris.
• Over speed:
– The pump rotor is driven by an external flow above the maximum allowed value.
▶ Ensure that there is no other external flow (additional secondary pump running) on the system.
• Over current:
– Abnormal current exceeding the limit.
▶ Check for leakage on appliance.
• Module over temperature:
– Temperature inside the
motor is too high.
▶ Check for evidence of dry running, low system pressure and ambient temperature.
• Turbine mode:
– The pump is driven by external flow (>1200l/h) in
opposite direction of its flow.
▶ Ensure that the external flow is less than 1200l/h.
Red - continuousPump stoppedThe pump has stopped due to permanent failure.• Faulty electronic module and/or faulty motor.▶ Restart the appliance and wait 30 seconds before switching back ON.
▶ Replace pump if LED is still red
after power restart.
No LEDNo power supplyNo voltage on electronics• Pump is not connected to mains
supply
▶ Check cable connection and
supply to pump.
• Faulty LED▶ Check if pump is running.
• Faulty electronics▶ Replace pump.

Faults that are not Displayed

Appliance faults Remedy
Combustion noises too loud; rumbling noises ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the ratio control valve; replace if required.
▶ Check condense drain is clear.
▶ Check fan depression.
Flow noises ▶ Set the pump rate or pump characteristic map correctly and match to the maximum output.
Heat-up takes too long. ▶ Set the pump rate or pump characteristic map correctly and match to the maximum output.
▶ Check system is balanced.
▶ Check anti-cycle time.
Flue gas values incorrect; CO content too high. ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the ratio control valve; replace if required.
Delayed ignition, poor ignition. ▶ Check the ignition transformer function for misfiring in Menu 6, replace if required.
▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check operation of meter governor.
▶ Check the power supply.
▶ Check the electrodes; replace if required.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the burner, replace if required.
▶ Check the air/gas ratio control valve; replace if required.
Condensate in air box ▶ Check the non-return valve in the air/gas manifold, replace if required.
No hot water. ▶ Check the turbine, replace if required.
▶ Check diverter valve
▶ Check for cross-piping.
DHW volume is not reached. ▶ Check the plate heat exchanger.
▶ Check flow device.
▶ Check silencer body.
No function, the display remains dark. ▶ Check the electrical wiring for damage.
▶ Replace defective cables.
▶ Check the fuse, replace if required.

Worcester Bosch Greenstar Si Compact Gas Boiler Fault Codes

FAULT CODES
Should a fault develop with this boiler (or the system), the boiler will enter a locking or blocking condition, and fault code information will be generated as described in this section.
Locking error The boiler display will flash a warning triangle and fault code. At the same time, a (static) cause code will also be displayed. Manual intervention is required following clearance of the fault:
▶ Press the reset button on the boiler fascia
Blocking error The boiler will stop operating with no-fault data displayed. The cause code, in the info menu, is accessed by pressing the spanner/ return button. The condition will clear automatically when the associated fault clears e.g. waiting for an area to cool. In some cases a
blocking error has a defined time duration prior to changing to a locking condition.
Fault code Alphanumeric code indicating the fault group
Cause code Three-digit number. During a blocking error (or normal operating status) it is not displayed but accessed in the info menu via the
spanner/return button. During a locking error, the cause code flashes on the display.
Maintenance
codes
These are displayed with the letter H followed by a number. The code advises of a situation that will need some attention but is not a fault that will stop the boiler from functioning. Some of the common ones are listed:
H11 H13 Hot water outlet sensor defect, hot water can still be delivered but with less control (sensor open/short circuit or out of position)
A time has been set in the Service interval function i.e. 1 to 72 months and that time has expired. Menu 2.5F allows this feature to be
set (1 to 72), a 0 will disable this function.

Worcester Greenstar Si Compact Gas Boiler Locking Errors

Worcester Greenstar Si Compact Gas Boiler Blocking Errors

Worcester Greenstar Si Compact Gas Boiler Locking Errors

Fault codesCause codesDescriptionReset typePossible cause
9A362HCM (Heat Control Module)Reset buttonIncorrect HCM fitted
9U233HCM (Heat Control Module)Reset buttonProblem with the code plug (faulty or not connected)
b7257Internal errorReplace control board.
C6215Fan problemReset buttonFan running too fast
216Fan problemReset buttonFan running too slow
C7214Fan problemReset buttonFan not running
217No airflow after a defined period of
time
Reset buttonFan not running or airflow blocked
D1240Return sensor errorReset buttonSensor wet or damaged (the boiler will block for 300 seconds
before this condition).
241Return sensor errorReset buttonSensor disconnected or damaged (the boiler will block for 300
seconds before this condition).
286Return temperature too highReset buttonBoiler overheat
E2222Flow sensor short circuitReset buttonFlow sensor shorted or damaged.
223Flow sensor open circuitReset buttonFlow sensor disconnected or damaged.
E5218Flow temperature too highReset buttonPrimary flow sensor overheated
332Primary flow sensor has exceeded
110°C
Reset buttonPrimary flow sensor overheated
E9219Safety sensor temperature too highReset buttonThe main heat exchanger has overheated.
Maximum temperature 105C°
220Safety sensor short circuitReset buttonMaximum temperature sensor on the main heat exchanger has
failed.
221Safety sensor open circuitReset buttonMaximum temperature sensor on the main heat exchanger has not
been recognised.
224Max temperature thermostat
activated
Reset buttonFlue gas thermostat overheat
EA227No flame detected after ignitionReset buttonFailure of four ignition attempts. The boiler waits 30 seconds before
another attempt is made.
229Loss of flame signal during operationReset buttonAn established flame has been extinguished. This could be caused by:
• moisture in the sump, due to a blocked sump/condensate trap.
• a strong wind into the flue.
234Gas valve errorReset buttonGas valve coil disconnected
261Ignition timing errorReset buttonFlame not established during the first 4 seconds ignition period.
F0237 - Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
239Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
242 - Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
256Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
258Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
259
262
263
Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
267Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
272Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
279Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
290Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
278Sensor test failedReset buttonOn power up all safety sensors are checked.
Check has failed.
280Recycle time errorReset buttonAfter the burner has stopped, the recycle mode purges gas from the heat exchanger before attempting to burn again. The software has
3.1 seconds to intervene before the boiler goes into this fault condition.
338Too many short burner starts without
confirmation
Reset buttonThere is an error where the pump is not detecting water.
F7228Flame errorReset buttonFalse flame. Flame detected before burner start.
328Internal errorReplace control board
FA306False flame errorReset buttonFlame detected after burner stop
FD231Mains power errorReset buttonElectrical power interruption.
FA364Gas valve EV2 leak test failedReset buttonGas valve leak.
Fb365Gas valve EV1 leak test failedReset buttonGas valve leak.

Worcester Greenstar Si Compact Gas Boiler Blocking Errors

Fault codeCause codeDescriptionPossible cause
A1281Pump stuck or running in airLittle or no water in the system.
C1264Airflow stopped during operationFan has stopped.
C4273Airflow present during last 24 hoursFan has been running continuously during the past 24 hours.
D1240Return sensor short circuit
241Return sensor disconnected
D4271Temperature difference between flow and
safety sensors exceeds limit
The temperature of the primary flow and the safety sensor on the WB7 should
be within 15°C of each other.
E9224MAX thermostat activatedFlue gas thermostat overheat.
276Flow temperature exceeds 95°CPrimary overheat - boiler waits for temperature to reduce; if not it becomes a
Locking error.
277Safety temperature exceeds 95°CMain heat exchanger safety sensor overheat - boiler will wait for the
temperature to reduce; if not it becomes a Locking error 219.
285Return temperature exceeds 95°CThe boiler will stop the burn and wait to see if it cools down. If after 2 seconds
there is an increase in temperature the boiler will go to Locking error 286.
EA227No ionisation detected after ignitionNo flame is detected. The boiler will block during 4 attempts before going to
Locking fault.
EF349Central heating, boil detect.
Large delta T despite minimum burner.
The boiler is operating at minimum burner load and there is a greater than
18°C Flow & Return temperature difference.
No code212Safety or flow temperature rises too fastAir lock or reduced water content.
213Temperature difference between supply and
return exceeding limit
Air lock or reduced water content.
260No temperature rise after burner startsSensor disconnected or no water content.
380Inlet DHW temperature higher than the DHW outlet temperature.The output is blocked until the inlet temperature drops below the output temperature.

Worcester Bosch Greenstar i Gas System Boiler Fault Codes

FAULT CODES
Should a fault develop with this boiler (or the system), the boiler will enter a locking or blocking condition, and fault code information will be generated as described in this section.
Locking error The boiler display will flash a warning triangle and fault code. At the same time a (static) cause code will also be displayed. Manual intervention is required following clearance of the fault:
▶ Press the reset button on the boiler fascia
Blocking error The boiler will stop operating with no fault data displayed. The cause code, in the info menu, is accessed by pressing the spanner/ return button. The condition will clear automatically when the associated fault clears e.g. waiting for an area to cool. In some cases a
blocking error has a defined time duration prior to changing to a locking condition.
Fault code Alpha numeric code indicating the fault group
Cause code Three digit number. During a blocking error (or normal operating status) it is not displayed, but accessed in the info menu via the
spanner/return button. During a locking error the cause code flashes on the display.
Maintenance
codes
These are displayed with the letter H followed by a number. The code advises of a situation that will need some attention but is not a fault that will stop the boiler from functioning. Some of the common ones are listed:
H11 H13 Hot water outlet sensor defect, hot water can still be delivered but with less control (sensor open/short circuit or out of position)
A time has been set in the Service interval function i.e. 1 to 72 months and that time has expired. Menu 2.5F allows this feature to be
set (1 to 72), a 0 will disable this function.

Worcester Bosch Greenstar i Gas System Boiler Locking Errors

Worcester Bosch Greenstar i Gas System Boiler Blocking Errors

Worcester Bosch Greenstar i Gas System Boiler Locking Errors

Fault codesCause codesDescriptionReset typePossible cause
9A362HCM (Heat Control Module)Reset buttonIncorrect HCM fitted
9U233HCM (Heat Control Module)Reset buttonProblem with the code plug (faulty or not connected)
b7257Internal errorReplace control board.
C6215Fan problemReset buttonFan running too fast
216Fan problemReset buttonFan running too slow
C7214Fan problemReset buttonFan not running
217No airflow after a defined period of
time
Reset buttonFan not running or airflow blocked
D1240Return sensor errorReset buttonSensor wet or damaged (the boiler will block for 300 seconds
before this condition).
241Return sensor errorReset buttonSensor disconnected or damaged (the boiler will block for 300
seconds before this condition).
286Return temperature too highReset buttonBoiler overheat
E2222Flow sensor short circuitReset buttonFlow sensor shorted or damaged.
223Flow sensor open circuitReset buttonFlow sensor disconnected or damaged.
E5218Flow temperature too highReset buttonPrimary flow sensor overheated
332Primary flow sensor has exceeded
110°C
Reset buttonPrimary flow sensor overheated
E9219Safety sensor temperature too highReset buttonThe main heat exchanger has overheated.
Maximum temperature 105C°
220Safety sensor short circuitReset buttonMaximum temperature sensor on the main heat exchanger has
failed.
221Safety sensor open circuitReset buttonMaximum temperature sensor on the main heat exchanger has not
been recognised.
224Max temperature thermostat
activated
Reset buttonFlue gas thermostat overheat
EA227No flame detected after ignitionReset buttonFailure of four ignition attempts. The boiler waits 30 seconds before
another attempt is made.
229Loss of flame signal during operationReset buttonAn established flame has been extinguished. This could be caused by:
• moisture in the sump, due to a blocked sump/condensate trap.
• a strong wind into the flue.
234Gas valve errorReset buttonGas valve coil disconnected
261Ignition timing errorReset buttonFlame not established during the first 4 seconds ignition period.
F0237 - Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
239Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
242 - Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
256Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
258Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
259
262
263
Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
267Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
272Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
279Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
290Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
278Sensor test failedReset buttonOn power up all safety sensors are checked.
Check has failed.
280Recycle time errorReset buttonAfter the burner has stopped, the recycle mode purges gas from the heat exchanger before attempting to burn again. The software has
3.1 seconds to intervene before the boiler goes into this fault condition.
338Too many short burner starts without
confirmation
Reset buttonThere is an error where the pump is not detecting water.
F7228Flame errorReset buttonFalse flame. Flame detected before burner start.
328Internal errorReplace control board
FA306False flame errorReset buttonFlame detected after burner stop
FD231Mains power errorReset buttonElectrical power interruption.
FA364Gas valve EV2 leak test failedReset buttonGas valve leak.
Fb365Gas valve EV1 leak test failedReset buttonGas valve leak.

Worcester Bosch Greenstar i Gas System Boiler Blocking Errors

Fault codeCause codeDescriptionPossible cause
A1281Pump stuck or running in airLittle or no water in the system.
C1264Airflow stopped during operationFan has stopped.
C4273Airflow present during last 24 hoursFan has been running continuously during the past 24 hours.
D1240Return sensor short circuit
241Return sensor disconnected
D4271Temperature difference between flow and
safety sensors exceeds limit
The temperature of the primary flow and the safety sensor on the WB7 should
be within 15°C of each other.
E9224MAX thermostat activatedFlue gas thermostat overheat.
276Flow temperature exceeds 95°CPrimary overheat - boiler waits for temperature to reduce; if not it becomes a
Locking error.
277Safety temperature exceeds 95°CMain heat exchanger safety sensor overheat - boiler will wait for the
temperature to reduce; if not it becomes a Locking error 219.
285Return temperature exceeds 95°CThe boiler will stop the burn and wait to see if it cools down. If after 2 seconds
there is an increase in temperature the boiler will go to Locking error 286.
EA227No ionisation detected after ignitionNo flame is detected. The boiler will block during 4 attempts before going to
Locking fault.
EF349Central heating, boil detect.
Large delta T despite minimum burner.
The boiler is operating at minimum burner load and there is a greater than
18°C Flow & Return temperature difference.
No code212Safety or flow temperature rises too fastAir lock or reduced water content.
213Temperature difference between supply and
return exceeding limit
Air lock or reduced water content.
260No temperature rise after burner startsSensor disconnected or no water content.
380Inlet DHW temperature higher than the DHW outlet temperature.The output is blocked until the inlet temperature drops below the output temperature.

Worcester Bosch Greenstar 8000 Gas Boiler Fault Codes

Fault Codes

Fault codeFault categoryDescriptionRemedy
200OBoiler in heating modeOperating message, is not a fault.
201OBoiler in hot water modeOperating message, is not a fault.
202OBoiler in anti-cycle modeOperating message, is not a fault.
203OBoiler in standby, no heat energy demandOperating message, is not a fault.
204OCurrent prim. water temp. higher than set val.The actual boiler water temperature is higher than the target boiler water temperature. The boiler is switched off.
208OChimney sweep demandOperating message, is not a fault.
214VFan shut down during safety time1. Reset the appliance.
2. Create a heat demand does the boiler fire up.
3. Check the voltage to the fan and the continuity of the fan harness.
4. Check the power modulation on the fan.
5. PCB is may be defective.
224VSafety temp. limiter has tripped1. Check if lead disconnected from the safety temperature limiter.
2. Check the high limit of the safety temperature limiter and the harness for continuity.
3. Check the flow temperature to confirm actual temperature (may tripped out at lower temperature, leading to safety temperature limiter fault)
4. Check the system pressure and top up as required.
5. Check if air trapped in the system and in the boiler.
6. Pump seized/not running: check the pump for failure or if she blocked.
7. Check if blockage/restriction within boiler/pipe work restricting the flow.
227VNo flame signal after ignitionTip: Check the ceramic insulator is not damaged, this can cause the spark to earth, twist and pull the ceramic insulator to ensure it is not broken.
1. Check the gas supply to property and the inlet on the gas valve.
2. Check the low pressure when the gas valve opens.
3. Gas valve failing to open: check for voltage to the valve and for possible blockage on inlet filter of the gas valve.
4. Obstruction in the air intake to the fan leading to incorrect CO2 ratio. Diaphragm is damaged or stucked.
5. Condensate trap is blocked or restricted. Condensate pipe is frozen.
6. Flue is blocked or restricted.
7. Heat exchanger is blocked or restricted.
8. Check the burner for damage.
9. Check the spark electrode or the lead failure. 10.Check the flame sense or the lead failure.
11.Check the rectification ground (black wire to heat exchanger).
228VFlame signal without flame presentTip: Check the ceramic insulator is not damaged, this can cause the spark to earth, twist and pull the ceramic insulator to ensure it is not broken.
1. Check the flame sense and the lead and replace if required.
2. Check the earth tags on the boiler and on the electrodes.
3. Check the operation of the siphon and no water collecting in the sump.
4. Replace the air and/or gas ratio control valve.
5. Replace the control unit and/or burner control unit.
229BFlame failed during burner operationTip: Check the ceramic insulator is not damaged, this can cause the spark to earth, twist and pull the ceramic insulator to ensure it is not broken.
1. Check the gas supply to the property and check the working pressure on the gas valve inlet.
2. Check the gas-air ratio.
3. Check the ionisation electrode and the harness for damage or contamination.
4. LPG: Sufficient gas in the tank or recently refilled?
232BBoiler locked by external switching contactExternal cut off switch not used in UK: Ensure nothing is plugged into red I3 connection.
1. Connection plug for external switch contact is not plugged into PCB.
2. There is no feedback voltage at the external safety contact at the condensate lifting pump blocks the heat generator.
3. Switching point for the external temperature monitor is set too low.
4. Connection cable to the external temperature monitor is damaged.
5. External temperature monitor is defective.
233VBoiler identification module or device electronics faulty1. Wrong code plug is inserted.
2. Check the code plug is not damaged.
3. Replace the code plug if required.
234VGas valve electrical fault1. Check the gas supply to the property and the inlet on the gas valve (check drop on inlet).
2. Check the connections on the gas valve and the board (loose connection).
3. Check the continuity down harness and replace if required.
4. Check the voltage to the gas valve (19‒24 V DC approx. when demand).
5. Check for water on the gas valve connections.
6. Check the resistance on the gas valve (pins 1‒2 approx. 69, 5 Ohms).
7. Replace the gas valve if resistances are incorrect.
8. If all tests are correct: replace the PCB.
235VConflicting versions of boiler electr. And boiler identificationReplace the code plug or the burner control.
237VSystem fault1. Check the code plug is not damaged.
2. Replace the code plug if required.
3. Replace the control unit (PCB).
238VBoiler electronics faulty1. Check the gas supply to the property and the inlet on the gas valve (check drop on inlet).
2. Check the connections on the gas valve and the board (loose connection).
3. Check the continuity down harness and replace if required.
4. Check the voltage to the gas valve (19‒24 V DC approx. when demand).
5. Check for water on the gas valve connections.
6. Check the resistance on the gas valve (pins 1‒2 approx. 69, 5 Ohms).
7. If all tests are correct: replace the PCB.
245State out of range1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
249VInternal software error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
250VDefault software error1. Restart the appliance to see if problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
251VFlash test error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
252VStack overflow1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
253VRAM test error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
254VEeprom test error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
258VInternal watchdog error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
259VAD reference error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
262VInternal OS error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
263VProgram sequence error1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Check the code plug is not damaged.
4. Replace the code plug if required.
5. Replace the control unit (PCB).
265BHeat demand lower than energy suppliedNot applicable, operating message, is not a fault.
268ORelay test was activatedNot applicable, status message.
269VFlame monitoring1. Restart the appliance to see if the problem re-occurs.
2. Check the electrical connections on the board (check for loose wires etc.).
3. Replace the control unit (PCB).
273BOperation of burner and fan interruptedNot applicable, status message.
281BPump pressure increase too low1. Check the flow pressure in system.
2. Check the system for circulation issues (air locks, blockage, restriction).
3. Check that the tacho cable plug for the circulation pump is fitted correctly.
4. Check the tacho cable for continuity and replace the tacho cable if required.
5. Replace the pump.
283OBurner startingOperating message, is not a fault.
284OOpening air/gas ratio control valve/oil solenoid valvesOperating message, is not a fault.
305OBoiler in hot water anti-cycle modeAnti-fast cycle mode, domestic hot water keep warm function.
1. Diverter valve is held in the hot water position for a period of time.
2. Check for false demands on the cold water inlet.
306VFlame signal after closing the fuel supplyTip: Ensure the working pressure returns immediately to the standing pressure when the gas valve closes.
1. Check the gas supply to the property and the inlet on the gas valve (check drop on inlet).
2. Check the gas valve is not passing and replace if required.
3. Replace the PCB.
352Test blocking errorFlue gas pressure module (FOM) is defective or interrupted.
353Test non-volatile lockoutDevice may not start temporarily, never been off for 20 min for 24 h.
354Test volatile lockoutOverpressure setting is detected.
357OVentilation programOperating message, is not a fault: Venting program has been activated.
358OAnti-seizing functn. activeOperating message, is not a fault: blocking protection for the heating pump and the 3-way valve is active.
360VIncomparable code plug1. Wrong code plug is inserted.
2. Check the code plug is not damaged.
3. Replace the code plug if required.
362VBoiler identification module or boiler electronics faulty1. Wrong code plug is inserted.
2. Check the code plug is not damaged.
3. Replace the code plug if required.
363VIonisation current did not drop during ionisation test1. Check and replace the ionisation cable.
2. Check and replace the electrodes if required.
3. Check and replace the control unit and/or burner control unit.
815WLow loss header temp. sensor faultyTip: Check menu has not been accidently switched on.
Moisture on the connectors – PCB fault.
1010ONo BUS communication1. Check the HMI plug on far right of the PCB (low voltage connection).
2. If using the Key: Check the Key connections (black, white, red, green) are plugged in to the correct position on the PCB. (Next to orange BUS connection leaving one space.) Check the pins on the plug.
3. Check the bridging links are in LR & 230 V out.
4. Replace the board.
5. Occasionally the Key connection (green flap) can cause this.
6. Check the 230 V external wiring does not run alongside the BUS connections.
1013Max. combustion point reached1. Check the maintenance menu.
2. Reset the maintenance code via the reset menu.
1017WSystem pressure too low1. Top up water and vent the system.
2. Check the voltage to the pressure sensor and the signal back from the pressure sensor.
3. Replace the pressure sensor.
1018Maintenance interval expired1. Check the maintenance date set in the menu.
2. Reset the maintenance code via the reset menu.
1019Incorrect pump type detected1. Pump communication failure or wrong pump is fitted (non-ErP).
2. Check the pump communication wire is connected and has continuity.
3. Replace the pump for correct modulating pump.
1021BCylinder charging or hot water temperature sensor faulty1. Check the domestic hot water temperature sensor connected and the plug connected to temperature sensor.
2. Check the resistance of the temperature sensor and replace if required.
3. Check the continuity of harness and replace if required.
1023Maximum run time including standby time reached1. Check the maintenance menu.
2. Reset the maintenance code via the reset menu.
1025Return temp. sensor is faultyNot fitted on the boiler.
1037WOutside temp. sensor faulty - heating back- up operation activeTip: Check the weather compensation is applicable and the menu has not been accidently switched on in the menu.
1. Check the positioning of the outside weather sensor.
2. Check the weather sensor connections on the control board.
3. Check the resistance of the sensor and the continuity down the cable and replace if required.
1065BSystem pressure sensor faulty or not connected1. Check the water pressure sensor plug is connected.
2. Plug the connection plug on the water pressure sensor correctly.
3. Check the continuity of harness and replace if required.
4. Check the voltage to the pressure sensor and the return voltage to the pressure sensor.
5. Replace the pressure sensor.
1068WOutside temp. sensor or lambda probe faulty1. Check the outdoor sensor plug is connected.
2. Check the resistance of the sensor and replace if required.
3. Check the continuity of harness and replace if required.
4. Replace the outdoor sensor.
1070The next maintenance is due on
please call your installer. phone
Advanced service reminder warning.
1. Check the maintenance menu.
2. Reset the maintenance code via the reset menu.
1071The next maintenance is now due please call your installer. phone 1. Check the maintenance menu.
2. Reset the maintenance code via the reset menu.
1072Maintenance is overdue please call your installer. phone 1. Check the maintenance menu.
2. Reset the maintenance code via the reset menu.
1073WShort circuit of the flow temperature sensor1. Check the flow temperature sensor plug is connected.
2. Check the resistance of the flow temperature sensor and replace if required.
3. Check the continuity of harness and replace if required.
4. Replace the flow temperature sensor.
1074WNo signal from flow temperature sensor1. Check the flow temperature sensor plug is connected.
2. Check the resistance of the flow temperature sensor and replace if required.
3. Check the continuity of harness and replace if required.
4. Replace the flow temperature sensor.
5. Replace the PCB.
1075WShort-circuit heat exchanger temperature sensor1. Check the temperature sensor plug is connected.
2. Check the resistance of sensor and replace if required.
3. Check the continuity of harness and replace if required.
4. Replace the temperature sensor.
5. Replace the PCB.
1076WNo signal from heat exchanger temperature sensor1. Replace the temperature sensor plug is connected.
2. Check the resistance of sensor and replace if required.
3. Check the continuity of harness and replace if required.
4. Replace the temperature sensor.
5. Replace the PCB.
2085VInternal fault1. Reset the appliance.
2. Switch off the appliance for 30 s then turn back on.
3. Check the incoming mains voltage.
4. Check the polarity.
5. Replace the PCB.
2908VSystem fault boiler electronics/basic controller1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective and must be
replaced.
2910VFault in flue system1. Check the flue for obstructions and remove any found.
2. Check the flue integrity test.
3. Check for water in the sump and check the siphon operation.
2914There is no communication between the appliance controller and burner module1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective.
2915VThe fan keeps running after the post purge1. Reset the appliance.
2. Create a heat demand does the boiler fire up.
3. Check the voltage to the fan and the continuity of the fan harness.
4. Check the power modulation on the fan.
5. PCB is may be defective.
2916VGas valve was detected to be open during post purge1. Carry out a localised tightness test on the gas valve and replace if required.
2. Check the voltage to gas valve.
3. The gas valve or the PCB may have a fault.
2920VFault in flame monitoringPossible PCB fault, no checks available.
2923VUnexpected feedback from the modulating/
current controlled gas valve
Possible PCB fault, no checks available.
2924VNo feedback from the gas valve1. Check the voltage to the gas valve.
2. Check the resistance of the gas valve coils.
3. Check the continuity of harness and replace if required.
4. The gas valve or the PCB may have a fault.
2925VToo low feedback from the modulating gas valve1. Check the voltage to the gas valve.
2. Check the resistance of the gas valve coils.
3. Check the continuity of harness and replace if required.
4. The gas valve or the PCB may have a fault.
2926VToo high feedback from the modulating/ current controlled gas valve1. Check the voltage to the gas valve.
2. Check the resistance of the gas valve coils.
3. Check the continuity of harness and replace if required.
4. The gas valve or the PCB may have a fault.
2927BFlame failed during burner operation1. Check the gas supply to the property and the inlet on the gas valve (check drop on inlet) and replace if required.
2. Check the flame sense probe and the earth to the heat exchanger.
3. Check the voltage to the gas valve and the continuity of harness and replace if required.
4. Check the condition of the bearing plate.
5. Check the flame sense plug is connected and the continuity of harness and replace if required.
6. Check the fan pressure.
7. Check the siphon trap and the discharge route.
8. Check the flue integrity test.
2928Internal error1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective.
2931Illegal instruction executed by microcontroller1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective.
2940VLow voltage1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective.
2946VIncorrect code plug detected1. Check the code plug and the part number.
2. Check the code plug connections for damage.
3. Replace the code plug.
2948BNo flame signal with low outputThe burner starts automatically after purging. It may cause strong winds.
1. If the fault occurs repeatedly: check the settings of the CO2 values.
2. Check the flue integrity.
3. Check the flue terminal.
2949BNo flame signal with high outputIt may cause strong winds or flue gas recirculation. The burner starts automatically after purging.
1. Check the flue integrity.
2. Check the flue terminal position.
3. Check the CO2 settings and adjust.
4. Check the burner and the heat exchanger gaskets and the inner flue gaskets.
5. Check the gas pressure during burning at full load (working pressure, dropping low).
2950BNo flame signal following starting procedure1. Check the CO2 settings and adjust.
2. Check the burner and the heat exchanger gaskets.
3. Check the gas pressure during burning at full load.
4. Burner restarts automatically after purging.
2951VLoss of flame too many timesNote: Combustion case off can case this fault.
1. Refer to blocking errors(s) that lead to this locking error. Check the fault history on the appliance.
2. Possibly the purging of the gas pipe is incomplete.
3. It could also indicate a wide variety of issues such as pipework undersized or gas pressure dropping off, incorrectly routed condens drains, incorrectly sited flues,
incorrectly wired etc.
2952VInternal fault when testing ionisation signal1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective.
2955BBoiler does not support the parameters set for the hydraulic configurationVerify that the following settings are correct. This can only be reset by powering off the appliance.
1. Low loss header setting = OFF
2. Internal DHW hydraulic = 1/ON
3. Heat circuit 1 hydraulic = 1/ON
4. CH hydraulic = 1/ON
2956OHydraulic configuration at the boiler activatedVerify that the following settings are correct. This can only be reset by powering off the appliance.
1. Low loss header setting = OFF
2. Internal DHW hydraulic = 1/ON
3. Heat circuit 1 hydraulic = 1/ON
4. CH hydraulic = 1/ON
2957VInternal burner control error1. Restart the appliance to see if the problem re-occurs.
2. If the fault remains after resetting: the burner controller (PCB) is defective and must be
replaced.
2961VNo fan signal available1. Check the mains voltage to the fan.
2. Check the fan harness for continuity and replace if required.
3. Check the pulse width modulation (PWM).
4. Replace the fan.
5. Replace the PCB.
2962VFan not running1. Check the mains voltage to the fan.
2. Check the fan harness for continuity and replace if required.
3. Check the pulse width modulation (PWM).
4. Replace the fan.
5. Replace the PCB.
2963BSignal from flow and heat exchanger temperature sensor outside the permissible range1. Check the flow through the appliance and the system is filled.
2. Check for air locks in the system and purge if required.
3. Check the heat exchanger sensor (primary thermistor) and the plug connected to temperature sensor.
4. Check the resistant of the temperature sensor and replace if required.
5. Check the continuity of harness and replace if required.
2964BFlow rate in heat exchanger too low1. Supply sensor is not on the supply pipe.
2. Supply sensor does not make proper contact to the supply pipe.
3. Check the sensor and the flow sensor are making contact with the pipework.
4. Check the system filled with water.
5. No water flow, because the CH system is closed.
6. No water flow, because the pump is not operating correctly.
2965BFlow temperature too high1. Check the flow through the appliance and the system is filled.
2. Check for the air locks in the system and purge if required.
3. Check the isolation valves.
2966BFlow temperature rise in heat exchanger too rapid1. Check the flow through the appliance and the system is filled.
2. Check for the air locks in the system and purge if required.
3. Check the isolation valves.
4. Check the pump is operating freely and check the voltage to the pump.
2967BFlow/heat exchanger temperature sensor differential too great1. Check the flow through the appliance and the system is filled.
2. Check for air locks in the system and purge if required.
3. Check the isolation valves.
4. Check the pump is operating freely and check the voltage to the pump.
5. Check the heat exchanger sensor and the flow sensor are making contact with the pipework.
6. Check the heat exchanger sensor and the resistance of the temperature sensor and replace if required.
7. Check the continuity of harness and replace if required.
2968ORefilling system pressureThe auto filling function is active. The filling valve opens in order to feed fresh water to the
heating system automatically.
2969Maximum number of refills reachedThe maximum number of refills has been reached.
2970BPressure drop in heating system too rapidToo many unexpected pressure drops within a short time period.
1. Cause code can appear if system is pressurised and the intelligent filling loop activated and then the system vented.
2. Switch off the intelligent fill in the system menu, re-pressurise manually and vent the system.
3. Ensure the correct pressure. If cause code does not clear power off appliance.
2971BSystem pressure too lowCompare to internal pressure dial max. 0.5 bar pressure differential between them.
Top up water until the pre-set pressure reached.
Intelligent filling loop
1. Switch off the intelligent fill in the system menu, re-pressurise manually and vent the system.
2. Ensure the correct pressure then factory rest appliance. If cause code does not clear power off appliance.
Other filling loop
Vent the heating system and top up water until the pre-set pressure reached.
Pressure sensor
1. Check the continuity down harness for the pressure sensor and replace if required.
2. Check the voltage at the pressure sensor and replace if required.
2972Mains voltage too lowCheck the mains voltage on the appliance (L and N).
3071Comfort + II RF1. Check the configuration (address setting). The selected setting requires a remote control.
2. Check the EMS connection cable for the remote control for damage. The BUS voltage on the remote control must be between 12 and 15 V DC.
3. The remote control is defective.

Faults that are not Displayed

Appliance faults Remedy
Combustion noises too loud; rumbling noises ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the air/gas ratio control valve; replace if required.
Flow noises ▶ Set the pump rate or pump characteristic map correctly and match to the maximum
output.
Heat-up takes too long. ▶ Set the pump rate or pump characteristic map correctly and match to the maximum
output.
Flue gas values incorrect; CO content too high. ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the air/gas ratio control valve; replace if required.
Violent ignition, poor ignition. ▶ Check the ignition transformer with service function t01 for misfiring, replace if required.
▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the power supply.
▶ Check the electrodes with cable; replace if required.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ For natural gas: check the external gas flow monitor, replace if required.
▶ Check the burner, replace if required.
▶ Check the air/gas ratio control valve; replace if required.
Condensate in air box ▶ Check the non-return valve in the air-gas manifold, replace if required.
Combi boilers: hot water outlet temperature is not reached. ▶ Check the turbine, replace if required.
▶ Check the gas/air ratio.
Combi boilers: DHW volume is not reached. ▶ Check the plate heat exchanger.
No function, the display remains dark. ▶ Check the electrical wiring for damage.
▶ Replace defective cables.
▶ Check the fuse, replace if required.

Worcester Bosch Greenstar CDi Compact Gas Boiler Fault Codes

Fault codes
Should a fault develop with this boiler (or the system), the boiler will enter a locking or blocking condition, and fault code information will be generated as described in this section.
Locking error The boiler display will flash a warning triangle and fault code. At the same time, a (static) cause code will also be displayed. Manual intervention is required following clearance of the fault:
▶ Press the reset button on the boiler fascia
Blocking error The boiler will stop operating with no-fault data displayed. The cause code, in the info menu, is accessed by pressing the spanner/return button. The condition will clear automatically when the associated fault clears e.g. waiting for an area to cool.
In some cases a blocking error has a defined time duration prior to changing to a locking condition.
Fault code Alphanumeric number indicating the fault group
Cause code Three-digit number. During a blocking error (or normal operating status) it is not displayed, but accessed in the info menu via
the spanner/return button. During a locking error, the cause code flashes on the display.

Worcester Bosch Greenstar CDi Compact Gas Boiler Locking Errors

Worcester Bosch Greenstar CDi Compact Gas Boiler Blocking Errors

Locking Errors

Fault codesCause codesDescription Reset typePossible cause
9U233HCM (Heat Control Module)Reset buttonProblem with the code plug
b7257Internal errorReplace control board.
C6215Fan problemReset buttonFan running too fast
216Fan problemReset buttonFan running too slow
C7214Fan problemReset buttonFan not running
217No airflow after a defined period of timeReset buttonFan not running or airflow blocked
D1240Return sensor errorReset buttonSensor wet or damaged (the boiler will block for 300 secs before this
condition).
241Return sensor errorReset buttonSensor disconnected or damaged (the boiler will block for 300 secs
before this condition).
286Return temperature too highReset buttonBoiler overheat
E2222Flow sensor short circuitReset buttonFlow sensor shorted or damaged.
223Flow sensor open circuitReset buttonFlow sensor disconnected or damaged.
E5218Flow temperature too highReset buttonPrimary flow sensor overheated
332Primary flow sensor has exceeded
110°C
Reset buttonPrimary flow sensor overheated
E9219Safety sensor temperature too highReset buttonThe main heat exchanger has overheated.
Maximum temperature 105C°
220Safety sensor short circuitReset buttonMaximum temperature sensor on the main heat exchanger has failed.
221Safety sensor open circuitReset buttonMaximum temperature sensor on the main heat exchanger has not
been recognised.
224Max temperature thermostat activatedReset buttonFlue gas thermostat overheat
EA227No flame detected after ignitionReset buttonFailure of four ignition attempts. The boiler waits 30 seconds before
another attempt is made.
229Loss of flame signal during operationReset buttonAn established flame has been extinguished. This could be caused by:
• moisture in the sump, due to a blocked sump/condensate trap.
• a strong wind into the flue.
234Gas valve errorReset buttonGas valve coil disconnected
261Ignition timing errorReset buttonFlame not established during the first 4 seconds ignition period.
F0237 -
239
242 -
256
258
259
262
263
267
272
279
290
Internal errorCall Worcester, Bosch Group Technical helpline 0330 123 3366
278Sensor test failedReset buttonOn power up all safety sensors are checked. Check has failed.
280Recycle time errorReset buttonAfter the burner has stopped, the recycle mode purges gas from the heat exchanger before attempting to burn again. The software has 3.1
seconds to intervene before the boiler goes into this fault condition.
338Too many short burner starts without confirmationReset buttonThere is an error where the pump is not detecting water.
F7228Flame errorReset buttonFalse flame. Flame detected before burner start.
328Internal errorReplace control board
FA306False flame errorReset buttonFlame detected after burner stop
FD231Mains power errorReset buttonElectrical power interruption.
FA364Gas valve EV2 leak test failedReset buttonGas valve leak.
Fb365Gas valve EV1 leak test failedReset buttonGas valve leak.

Blocking Errors

Fault codeCause codeDescriptionPossible cause
A1281Pump stuck or running in airLittle or no water in the system.
C1264Airflow stopped during operationFan has stopped.
C4273Airflow present during last 24 hoursFan has been running continuously during the past 24 hours.
D1240Return sensor short circuit
241Return sensor disconnected
D4271Temperature difference between flow and safety sensors exceeds limitThe temperature of the primary flow and the safety sensor on the WB7 should bewithin 15°C of each other.
E9224MAX thermostat activatedFlue gas thermostat overheat.
276Flow temperature exceeds 95°CPrimary overheat - boiler waits for temperature to reduce; if not it becomes a Locking error.
277Safety temperature exceeds 95°CMain heat exchanger safety sensor overheat - boiler will wait for the temperature to reduce; if not it becomes a Locking error 219.
285Return temperature exceeds 95°CThe boiler will stop the burn and wait to see if it cools down. If after 2 seconds
there is an increase in temperature the boiler will go to Locking error 286.
EA227No ionisation detected after ignitionNo flame is detected. The boiler will block during 4 attempts before going to
Locking fault.
EF349Central heating, boil detect.
Large delta T despite minimum burrner.
The boiler is operating at minimum burner load and there is a greater than 18°C
Flow & Return temperature difference.
No code212Safety or flow temperature rises too fastAir lock or reduced water content.
213Temperature difference between supply and return exceeding limitAir lock or reduced water content.
260No temperature rise after burner startsSensor disconnected or no water content.
380Inlet DHW temperature higher than the DHW
outlet temperature.
The output is blocked until the inlet temperature drops below the output
temperature.

Worcester Bosch Greenstar CDi Highflow Gas Boiler Fault Codes

Fault Codes

Condensate Pump Operating Lights

Fault Codes

Display
code:
Fault descriptionCheck, repair/replace as necessary
A1Pump dry run detection or
Pump is running in air
Check the system pressure, refill if necessary
A5Tank NTC defectCheck tank NTC sensor and leads, measure resistance across NTC (33.5k - 500 )
A7DHW NTC defectCheck DHW NTC sensor and leads, measure resistance across NTC (33.5k - 500 )
A8EMS communication errorCheck electrical connections of EMS controls (if fitted), connections on the control board,
replace control board.
b1Code plug not detectedInsert code plug correctly, test and replace as necessary.
b2, b3, b4,
b5,b6
Data errorReplace control board.
b7Burner control errorReplace control board.
C6Fan defectCheck fan, lead, and connector, replace as necessary.
d3External temp limiterCheck plug connector ST8, link missing/damaged between 8 & 9 on ST8.
d5Condensate pump failureSee condensate pump table.
d6Internal heat bank overflowCheck system pressure, tank overheat thermostat and leads, and pump operation
EAFlame not detectedCheck gas is present and working gas pressure, ignition electrodes and harness, flame sense
electrode and harness, and operation of gas valve. Replace as necessary.
E2Primary NTC defectCheck primary NTC sensor and leads, resistance across NTC should be between 36k to 1k 
E9OH stat trippedCheck system pressure, over heat thermostat, and pump operation.
Check fuse (T1.6A slow blow), replace as necessary.
F0Internal errorCheck all electrical connections, replace control board as necessary.
F1ROM error checkCheck all electrical connections, replace control board as necessary.
F7Flame detected after appliance shut offCheck flame sense electrode and harness, and control board for signs of water damage. Replace as necessary
FAFlame detected after gas shut offCheck flame sense electrode and harness, and control board for signs of water damage.
Check gas valve operation. Replace as necessary
FdReset button pressedPress reset button again

Condensate Pump Operating Lights

Operating lamps
Cause
Solution
Green Red
Off Off Mains supply not connected
Power failure
Connect mains supply
Check mains and fuse/circuit breaker
Flashing Flashing Dry-run
(possible air in pump)
Pump restarts automatically after one minute
On Flashing Pump blocked Visually inspect the pump inlet and tank.
Remove or rinse out any dirt or foreign bodies
On On Level exceeds alarm level Discharge hose or non-return valve blocked Possible kink in discharge hose
(clean or remove kink if applicable)
Off Flashing Pump blocked and
alarm level exceeded
Visually inspect the pump inlet and tank.
Remove or rinse out any dirt or foreign bodies

Worcester Bosch Greenstar CDi Highflow Gas Boiler Fault Codes

Worcester Bosch Greenstar CDi Highflow Gas Boiler Fault Codes

Worcester Bosch Greenstar CDi Highflow Gas Boiler Condensate Pump Operating Lights

Fault Codes

Display
code:
Fault descriptionCheck, repair/replace as necessary
A1Pump dry run detection or
Pump is running in air
Check the system pressure, refill if necessary
A5Tank NTC defectCheck tank NTC sensor and leads, measure resistance across NTC (33.5k - 500 )
A7DHW NTC defectCheck DHW NTC sensor and leads, measure resistance across NTC (33.5k - 500 )
A8EMS communication errorCheck electrical connections of EMS controls (if fitted), connections on the control board,
replace control board.
b1Code plug not detectedInsert code plug correctly, test and replace as necessary.
b2, b3, b4,
b5,b6
Data errorReplace control board.
b7Burner control errorReplace control board.
C6Fan defectCheck fan, lead, and connector, replace as necessary.
d3External temp limiterCheck plug connector ST8, link missing/damaged between 8 & 9 on ST8.
d5Condensate pump failureSee condensate pump table.
d6Internal heat bank overflowCheck system pressure, tank overheat thermostat and leads, and pump operation
EAFlame not detectedCheck gas is present and working gas pressure, ignition electrodes and harness, flame sense
electrode and harness, and operation of gas valve. Replace as necessary.
E2Primary NTC defectCheck primary NTC sensor and leads, resistance across NTC should be between 36k to 1k 
E9OH stat trippedCheck system pressure, over heat thermostat, and pump operation.
Check fuse (T1.6A slow blow), replace as necessary.
F0Internal errorCheck all electrical connections, replace control board as necessary.
F1ROM error checkCheck all electrical connections, replace control board as necessary.
F7Flame detected after appliance shut offCheck flame sense electrode and harness, and control board for signs of water damage. Replace as necessary
FAFlame detected after gas shut offCheck flame sense electrode and harness, and control board for signs of water damage.
Check gas valve operation. Replace as necessary
FdReset button pressedPress reset button again

Condensate Pump Operating Lights

Operating lamps
Cause
Solution
Green Red
Off Off Mains supply not connected
Power failure
Connect mains supply
Check mains and fuse/circuit breaker
Flashing Flashing Dry-run
(possible air in pump)
Pump restarts automatically after one minute
On Flashing Pump blocked Visually inspect the pump inlet and tank.
Remove or rinse out any dirt or foreign bodies
On On Level exceeds alarm level Discharge hose or non-return valve blocked Possible kink in discharge hose
(clean or remove kink if applicable)
Off Flashing Pump blocked and
alarm level exceeded
Visually inspect the pump inlet and tank.
Remove or rinse out any dirt or foreign bodies

Worcester Bosch Greenstar 8000 Style Gas Boiler Fault Codes

Worcester Bosch Greenstar 8000 Style Gas Boiler Fault Codes

Worcester Bosch Greenstar 8000 Style Gas Boiler Faults that are not displayed

Fault Codes

Fault codeFault categoryDescriptionRemedy
200OBoiler in heating mode–
201OBoiler in hot water mode–
202OBoiler in anti-cycle mode–
203OBoiler in standby, no heat energy demand–
204OCurrent prim. water temp. higher than set val.–
208OChimney sweep demand–
224VSafety temp. limiter has tripped1. Open the closed valve in the heating circuit.
2. Top up water until the preset pressure is reached.
3. Connect the plug correctly to the safety temperature limiter.
4. Replace the safety temperature limiter.
227VNo flame signal after ignition1. Open the gas isolator.
2. Change the gas installation.
3. Replace the control unit/burner control unit.
4. Replace the ignition electrode.
5. Replace the monitoring electrode.
6. Replace the ignition cable.
7. Replace the ionisation cable.
8. Replace the air/gas ratio control valve.
9. Correct the burner setting.
228VFlame signal without flame present1. Replace the air/gas ratio control valve.
2. Replace the ionisation cable.
3. Replace the control unit/burner control unit.
305OBoiler in hot water anti-cycle mode–
306VFlame signal after closing the fuel supply1. Replace the air/gas ratio control valve.
2. Replace the ionisation cable.
3. Replace the control unit/burner control unit.
815BLow loss header temp. sensor faulty1. Check the sensor port.
2. Check the differential sensor for incorrect installation position or breakage.
1017WWater pressure too low1. Top up water and vent the system.
2. Replace the pressure sensor.
1021BHot water temperature sensor is defective1. Connect the plug to the hot water temperature sensor correctly.
2. Mount the hot water temperature sensor correctly.
3. Replace the hot water temperature sensor.
4. Replace the connecting lead to the hot water temperature sensor.
1037WOutside temperature sensor defectiveCheck the connecting lead.
1065BPressure sensor defective or not connected1. Connect the plug to the pressure sensor correctly.
2. Replace the connecting lead to the pressure sensor.
3. Replace the pressure sensor.
4. Replace the control unit.
1068WOutside temperature sensor defectiveCheck the connecting lead.
1073WShort circuit of the flow temperature sensor1. Replace the temperature sensor.
2. Replace the connecting lead to the temperature sensor.
3. Replace the control unit.
1074WNo signal from the flow temperature sensor available1. Connect the plug to the flow temperature sensor correctly.
2. Replace the flow temperature sensor.
3. Replace the connecting lead to the flow temperature sensor.
4. Replace the control unit.
1075WShort circuit of the temperature sensor at the heating block1. Replace the temperature sensor.
2. Replace the connecting lead to the temperature sensor.
3. Replace the control appliance.
1076WNo signal from the temperature sensor at the heating block available1. Replace the temperature sensor.
2. Replace the connecting lead to the temperature sensor.
3. Replace the control unit.
2920VFault in flame monitoring–
2927BFlame failed during burner operation1. Open the main shut-off valve.
2. Open the appliance shut-off valve.
3. Shut down the appliance and check the gas line.
4. Signal evaluation on printed circuit board defective.
5. Replace the ionisation electrode.
6. Establish protective conductor connection (PE) in the control unit.
7. Replace the ignition cable.
8. Replace the connecting lead to the ionisation electrode.
9. Replace the air/gas ratio control valve. 10.Set the burner correctly.
11.Set the burner at minimum rated load. 12.Check the integrity flue system.
13.The interconnected room air supply is too small or the size of the ventilation opening is too small.
14.Clean the heating block on the flue gas side.
15.Replace the control unit/burner control unit.
2946VIncorrect code plug detectedReplace the code plug.
2948BNo flame signal with low outputThe burner starts automatically after cleaning.
1. If the fault occurs repeatedly: check the settings of the CO2 values.
2950BNo flame signal following starting procedureThe burner starts automatically after cleaning.
1. Set the correct gas/air ratio correctly.
2963BSignal from flow and heat exchanger temperature sensor outside the permissible
range
Connect the connecting lead correctly.
2964BFlow rate in heat exchanger too low–
2965BFlow temperature too high–
2966BFlow temperature rise in heat exchanger too
rapid
–
2967BFlow/ heate exchanger temperature sensor
differential too great
–
2970BPressure drop in heating system too rapid–
2971BSystem pressure too low1. Vent the heating system.
2. Top up water until the preset pressure is reached.
3. Replace the cable to the pressure sensor.
4. Replace the pressure sensor.

Faults that are not Displayed

Appliance faults Remedy
Combustion noises too loud; rumbling noises ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the air/gas ratio control valve; replace if required.
Flow noises ▶ Set the pump rate or pump characteristic map correctly and match to the maximum
output.
Heat-up takes too long. ▶ Set the pump rate or pump characteristic map correctly and match to the maximum output.
Flue gas values incorrect; CO content too high. ▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the air/gas ratio control valve; replace if required.
Violent ignition, poor ignition. ▶ Check the ignition transformer with service function t01 for misfiring, replace if required.
▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check the power supply.
▶ Check the electrodes with cable; replace if required.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ For natural gas: check the external gas flow monitor, replace if required.
▶ Check the burner, replace if required.
▶ Check the air/gas ratio control valve; replace if required.
Condensate in air box ▶ Check the non-return valve in the air-gas manifold, replace if required.
Combi boilers: hot water outlet temperature is not reached. ▶ Check the turbine, replace if required.
▶ Check the gas/air ratio.
Combi boilers: DHW volume is not reached. ▶ Check the plate heat exchanger.
No function, the display remains dark. ▶ Check the electrical wiring for damage.
▶ Replace defective cables.
▶ Check the fuse, replace if required.

Worcester Bosch Greenstar Heatslave II Oil Boiler Fault Codes

Cause codeFault codeDescriptionReset typeBlockingLockingPossible cause/solution
210E9Maximum temperature thermostat or air pressure switch activatedResetXFlue gas or tank thermostat overheat. Reset the overheat thermostat or air pressure switch before resetting appliance.
212No codeSafety or flow temperature too highXAir lock or reduced water content.
218E5Flow temperature too highResetXPrimary sensor overheated, wait 30 minutes and try a reset.
219E9Safety temperature too highResetXThe main heat exchanger has overheated.
Maximum temperature 105°C, wait 30 minutes and try a reset.
220E9Safety sensor short circuitResetXMaximum temperature sensor on the main heat exchanger has failed.
221E9Safety sensor open circuitResetXMaximum temperature sensor on the main heat exchanger has not been recognised.
222E2Flow sensor short circuitResetXFlow sensor shorted or damaged, reconnect or replace as required.
223E2Flow sensor open circuitResetXFlow sensor disconnected or damaged, reconnect or replace as required.
233E2HCM (Heat Control Module)ResetXHCM Code plug missing or defective.
Refer to table 13, i22 and i23 to determine HCM number fitted
237F0Software relay errorResetXResistors between plug X4 pins 3 & 5 disconnected/>150k 
or water in the burner control box
238F0Software relay errorResetXResistors between plug X4 pins 3 & 5 disconnected/>150k 
or water in the burner control box
239F0Watchdog relay errorResetXIf the error persists, change the control board
259FOA/D reference relay errorResetXIf the error persists, change the control board
263F0Appliance powered off with locking fault presentResetXLocking fault still present when powered off/on, press the reset button to clear.
271D4Temperature difference between flow and safety sensors exceeds limitXThe temperature of the primary flow and the safety sensor on the main heat exchanger should be within 15°C of each other. Check the flow sensor is seated properly on the flow pipe.
276E9Flow temperature exceeds 95°CXPrimary overheat - boiler waits for temperature to reduce, wait approximately 30 minutes and try a reset.
277E9Safety temperature exceeds 95°CXMain heat exchanger safety sensor overheat - boiler waits for temperature to reduce, approximately 30 minutes.
278F0Sensor test errorResetXOn power up, all safety sensors are checked. Check has failed.
279F0A/D converter errorResetXIf the error persists, change the control board
290F0A/D converter reference errorResetXIf the error persists, change the control board
332E5Primary flow has exceeded 105°CResetXPrimary sensor overheated.
359No CodeDHW outlet or storage tank exceeds 90°CXPump & burner are blocked until temperature drops to <89°C. wait approximately 30 minutes for temperature to drop.
3609AIncorrect HCM for boiler variantXReplace with the correct HCM.
Refer to table 13, i22 and i23 to determine HCM number fitted and select correct HCM number from list
380No codeInlet DCW temperature higher than DHW outlet temperatureXThe output is blocked until the inlet temperature drops below the output temperature, wait for approximately 30 minutes.
808A7DHW sensor defectiveResetXCheck and replace defect sensor as necessary
809A0Thermal store sensor defectiveResetXCheck and replace defect sensor as necessary
8559FBurner lock outResetXCheck the burner and fuel supply. Ensure the oil supply is free of contaminants.
8569F5 burner lockouts repeated resetsTurn boiler off/onXAfter Five 855 burner lock outs in one demand period, cause code 856 is displayed.
After boiler off/on cause code 263 will be displayed, press the reset button to clear this fault. another 5 burner lock resets can be attempted.
H29Warning triangle and House symbol displayed on controllerWeather compensation activated but no weather sensor detected, refer to section 5.11 on page 32 for more information.
H27Warning triangle symbol displayed on controllerDCW in sensor defect, (appliance operation not affected)

Worcester Bosch Greenstar 24/28/30 Gas Combi Boiler Fault Codes

Worcester Bosch Greenstar 24/28/30 Gas Combi Boiler Fault Codes

Worcester Bosch Greenstar 8000 Style Gas Boiler Faults that are not displayed

Fault Codes

Display Remedy
A7DHW temperature sensor faulty.Check the temperature sensor and connecting lead for breaks or short circuits.
A8Communication fault.Check BUS device connecting lead.
AdCylinder temperature sensor not detected.Check cylinder temperature sensor and connecting lead.
b1Code plug not detected.Insert code plug correctly, test and replace if necessary.
b2Internal data error.See servicing instructions for heating contractors.
b3
C6Fan not running.Check fan lead and connector, check fan, replace as necessary.
CCOutside temperature sensor not detected.Check outside temperature sensor and connecting lead for breaks.
d3External limiter has tripped.Temperature limiter TB1 has tripped. Jumper across 8-9 or PR-P0 is missing.
d5External primary NTC on low loss header defect.Check NTC and cable continuity.
E2Temperature sensor in CH flow faulty.Check the temperature sensor and connecting lead.
E9Heat exchanger temperature limiter or flue gas temperature limiter has tripped.
or
Flue pipe is blocked.
Check system pressure, temperature limiter, pump operation, fuse on PCB bleed appliance. Check water-side of heat exchanger. On appliances with displacement bodies in heat exchanger, check whether displacement bodies are fitted. Check the flue (fresh air or exhaust gas) pipe blockage, check air pressure switch and air pressure switch pipe. Check heat exchanger high limit stat and flue high limit stat.
EAFlame not detected.Is gas tap open? Check gas supply pressure, mains power connection, electrodes and leads, flue pipe, gas-air ratio.
On natural gas appliances, check external gas flow switch.
F0Internal fault.Check electrical connectors and ignition leads, replace PCB if necessary. Check
gas-air ratio.
F1Internal data error.See servicing instructions for heating contractors.
F7A flame is detected although the appliance is switched off.Check electrodes. Flue system OK? Check PCB for moisture.
FAA flame is detected after the gas has been switched off.Check gas valve. Clean condensate trap and check electrodes. Flue system OK?
FdReset was pressed in error.Press reset again.

Faults that are not Displayed

Appliance faults Remedy
Excessive combustion noise; rumbling noises ▶ Insert coding plug correctly. Replace if required.
▶ Check gas type.
▶ Check gas supply pressure. Adjust if required.
▶ Check flue system. Clean or repair if required.
▶ Check gas-air ratio in the combustion air and flue gas. Replace gas valve if required.
Flow noises ▶ Set pump stages or pump parameters correctly and match to maximum output.
Heat-up takes too long ▶ Set pump stages or pump parameters correctly and match to maximum output.
Flue gas readings incorrect; CO levels too high ▶ Check gas type.
▶ Check gas supply pressure. Adjust if required.
▶ Check flue system. Clean or repair if required.
▶ Check gas-air ratio in flue gas. Replace gas valve if required.
Ignition too strong, too weak ▶ Check gas type.
▶ Check gas supply pressure. Adjust if required.
▶ Check power supply.
▶ Check electrodes and leads. Replace if required.
▶ Check flue system. Clean or repair if required.
▶ Check gas-air ratio. Replace gas valve if required.
▶ For natural gas: Check external gas flow limiter. Replace if required.
▶ Check burner. Replace if required.
Set flow temperature exceeded ▶ Switch OFF automatic cycle block, i.e. set the value to 0.
▶ Set the required cycle block, e.g. standard setting of 3 minutes.
Condensate in air box ▶ Insert diaphragm in the mixing facility as per installation instructions. Replace if required.
DHW temperature is not reached ▶ Insert coding plug correctly. Replace if required.
▶ Check whether voltage (230 V AC) is present across terminal 1 and terminal 3. Repair if required.
▶ Check flow meter. Replace if required.
Control unit is flashing (i.e. all keys, all display
segments, burner indicator etc. are flashing)
▶ Replace fuse Si 3 (24 V).

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