Boiler Fault Code C (Flashing)

Also written as CFLASHING — same fault.

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

Fault code C (Flashing) appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has been manually or accidentally switched into a service testing mode, meaning it is running at a restricted low power level rather than responding to your heating demands. (As reported on Halstead Ace HE)