BoilerFaultCodes C1 51 High
Boiler Fault Code C1 51
Also written as C151 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code C1 51 appears across 1 boiler brand and 4 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 internal fan responsible for safety and combustion is not spinning at the correct speed, so it has shut down to prevent any risk. (As reported on Atag S 25CR)
Pick your boiler brand for the C1 51 fix
Source
Information for the C1 51 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