BoilerFaultCodes C33 Emergency
Boiler Fault Code C33
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code C33 appears across 3 boiler brands 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 an issue with the air supply or exhaust system, meaning it cannot safely remove combustion gases and has shut down to prevent a hazard. (As reported on Keston System 2 S30)
Pick your boiler brand for the C33 fix
Source
Information for the C33 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 7 July 2026