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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 15, 2024. Updated: February 15, 2024

Viessmann F4 Fault – How to fix it

Viessmann F4 Fault Code

Encountering an F4 error code on your Viessmann boiler signifies a problem with flame detection. This then locks you out for safety. This guide delves into the root causes of this issue, potential fixes, and the costs involved in rectifying the error.

Key Points

  • The F4 fault code indicates a failure in flame detection, leading to boiler lockout.
  • Possible causes include stuck gas valves, wiring issues, faulty flame sensors, burner jet blockage, malfunctioning ignition leads, or a defective PCB.
  • DIY repairs are not advisable; professional intervention by a Gas Safe Registered engineer is required.
  • Costs for repairs vary, with specific fixes ranging from £60 to £800, depending on the nature of the problem.
  • Viessmann warranties cover repairs or replacements due to manufacturing defects, subject to annual servicing by a certified engineer.

Diagnosing and Fixing the F4 Error

Attempting DIY repairs on an F4 fault is impractical and illegal due to the technical and safety complexities involved. Professional diagnosis and repair by a Gas Safe Registered engineer are mandatory, with costs varying based on the nature of the fault:

  • Gas valve issues: £230 to £460
  • Wiring or connection faults: £50 to £140
  • Flame sensor defects: £360 to £490
  • PCB problems: £60 to £250 for fixes, £510 to £900 for replacements
  • Total boiler replacement (in cases of beyond economical repair): £2,100+ with finance options available

Warranty Coverage for F4 Fault Repairs

Viessmann Vitodens 050-W Combi Boiler B0KA - F4 Error | Boilerhut

Viessmann warranties typically cover defects arising from manufacturing or material flaws. However, warranty validity depends on adherence to terms such as annual servicing by certified professionals.

If Boilerhut installed your Viessmann boiler please call us before contacting Viessmann. In some circumstances, we can log in to your boiler to review the issues.


The F4 fault code on a Viessmann boiler indicates a potentially serious issue. It may require immediate attention from a qualified professional.

Ensuring compliance with warranty conditions through regular maintenance is also crucial for long-term boiler health and efficiency.

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