C1 High

Boiler Fault Code C1

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code C1 appears across 5 boiler brands and 33 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that the water leaving the unit is getting too hot too quickly, causing it to shut down to prevent damage. (As reported on Potterton Envoy 30)

Pick your boiler brand for the C1 fix

Alpha C1 2 models Potterton C1 1 model Remeha C1 2 models Vokera C1 3 models Worcester Bosch C1 25 models

Source

Information for the C1 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026