BoilerFaultCodesPotterton C4 Fault Code
The Potterton C4 fault code means: your boiler is simply cooling itself down by pushing leftover heat into your radiators after the burner has finished its cycle.. It appears on 1 Potterton model in our database.
Technical description: Main burner off, pump running to transfer remaining heat from boiler into the system
What causes the Potterton C4 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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Gas Safe Register →Potterton models that show the C4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton C4 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026