Low Information
C4 on Potterton Envoy 30

Your boiler is simply cooling itself down by pushing leftover heat into your radiators after the burner has finished its cycle.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Main burner off, pump running to transfer remaining heat from boiler into the system

What causes this fault?

This occurs when the boiler has finished heating and needs to dissipate the excess heat trapped inside the internal heat exchanger. The system keeps the pump running to push this leftover warmth into your radiators or hot water cylinder to prevent the unit from overheating. It is a standard safety and efficiency feature rather than a mechanical failure.

DIY fix possible

Wait a few minutes for the pump to finish its overrun cycleCheck that your room thermostat is not set too lowEnsure at least one radiator valve is open to allow heat to dissipate

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Related fault codes

C1View →C2View →

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