BoilerFaultCodes C4 / 273 High
Boiler Fault Code C4 / 273
Also written as C4273 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code C4 / 273 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 its exhaust fan has been running non-stop for the last day, so it has locked itself to prevent potential overheating or damage. (As reported on Worcester Bosch Greenstar i)
Pick your boiler brand for the C4 / 273 fix
Source
Information for the C4 / 273 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