BoilerFaultCodesPotterton C1 Fault Code
The Potterton C1 fault code means: your boiler has detected that the water leaving the unit is getting too hot too quickly, causing it to shut down to prevent damage.. It appears on 1 Potterton model in our database.
Technical description: Higher flow temperature
What causes the Potterton C1 fault?
This fault occurs when the water inside the boiler heats up much faster than the system can carry it away, often due to a blockage or a pump failure. It is essentially a safety mechanism that trips when the unit detects that the heat isn't being circulated properly into your radiators or hot water tank. Common culprits include a seized internal pump or a buildup of debris that has restricted the flow of water through the main heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after sitting idle all summer, which can cause the pump to stick.
DIY fix possible
Check that all radiator valves are fully open to allow water to circulate.Ensure the central heating bypass valve (if visible) is not closed.Check that the system pressure gauge is between 1 and 1.5 bar.
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Gas Safe Register →Potterton models that show the C1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton C1 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