How much does it cost to fix boiler error code C4?

Typical repair cost for the boiler C4 fault is £180-£450 including labour.

C4 High

Boiler Fault Code C4

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code C4 appears across 4 boiler brands and 15 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 is spinning too slowly to safely clear waste gases, so it has shut down as a precaution. (As reported on Worcester Bosch Greenstar 12i System)

Pick your boiler brand for the C4 fix

British Gas C4 1 model Sime C4 1 model Viessmann C4 3 models Worcester Bosch C4 10 models

Source

Information for the C4 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 31 August 2026