Save up to £590 PER YEAR on your heating billsGet Your FREE Online Quote Today
Save up to £590 PER YEAR a yearNeed a New Boiler?
Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 8, 2024. Updated: May 16, 2024

Combi Boiler Pipes Explained

The pipes of a combi boiler include two flow pipes, one for heating your home and one for hot water taps and showers. There is a return for the water coming back from the radiators and a mains cold water supply.

Then you have a gas supply pipe, plastic condensate pipe, pressure relief valve (which may be incorporated into the condensate pipe) and the flue (usually at the top or back of the boiler).

These different pipes ensure efficient water heating and distribution, safe disposal of gases and wastewater, and system pressure regulation.

Combi Boiler Pipes Overview

A combi boiler stands out for its ability to provide both heating and hot water from a single unit. They eliminate the need for additional hot and cold water storage. Its compactness and efficiency make it a preferred choice in many households. They offer space-saving benefits along with operational efficiency.

Combi boiler pipes explained | Boilerhut

Combi Boiler Pipes Explained

The functionality of a combi boiler is significantly attributed to its pipework, each serving a unique purpose:

  • Mains Water Pipe: Delivers cold water into the boiler. This is then heated for home heating and direct hot water use. A water softener or descaler might be necessary in areas with hard water to prevent limescale buildup.
  • Gas Supply Pipe: This boiler pipe supplies the necessary gas as fuel for heating the water. The type of gas (natural or LPG) affects the source and storage requirements.
  • Boiler Flue: Vents harmful combustion gases, such as carbon monoxide, outside. It ensures indoor air quality and safety.
  • Flow Pipes: There are two flow pipes; one directs heated water to radiators for space heating. The other supplies hot water to taps and showers. A diverter valve regulates the direction of the hot water, prioritising either heating or domestic hot water supply.
  • Return Pipes: Used radiator water is returned to the boiler for reheating via return pipes. This enhances system efficiency by utilising residual heat.
  • Condensate Pipe: This pipe expels wastewater produced during the heating process. Modern condensing combi boilers recycle heat from exhaust gases. This produces condensate that is safely disposed of through this pipe to a drain.
  • Pressure Relief Valve: This valve ensures system safety by releasing excess pressure. This prevents potential damage or hazards due to pressure buildup. Some boilers have a combined pressure relief valve and condensate pipe.
Combi boiler pipes explained | Boilerhut

Combi boiler pipes from a Boilerhut installation in early 2024.

Maintenance and Servicing

Combi boiler pipes are vital to the boiler’s workings, hot water, and heating. Condensing boilers must be serviced annually to maintain efficiency, safety, and longevity.

Either way, prompt attention to any issues that arise is important. This will prevent malfunctions and ensure a reliable heating and hot water supply.


You combi boilers pipes plays an integral role in its functionality. From ensuring efficient heating and water supply to maintaining safety standards. Regular maintenance and understanding the significance of each pipe can significantly contribute to the combi boiler’s optimal performance and durability.

Do you need a new boiler?

If you need a new or replacement boiler or are looking at having a central heating system installed, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

  • Next day boiler installation.
  • Instant, no-obligation quote in less than 1 minute.
  • Boiler finance options available for new boilers and central heating installation.
  • 10 to 12-year warranty on boilers.
  • ‘Excellent’ 5* customer satisfaction on Trustpilot.
  • Fixed prices. No hidden extras.
  • Get up to three quotes for different-tier boilers.

© Copyright - Boilerhut 2024 - Registered in England & Wales, company number: 8615540 Vat number: GB- 169 0436 95