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

Typical repair cost for the boiler C4 fault is £150-250 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 19 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is failing to confirm that its internal fan has stopped correctly, which is preventing it from starting up safely. (As reported on Worcester Bosch 537i)

Pick your boiler brand for the C4 fix

British Gas C4 1 model Sime C4 1 model Viessmann C4 3 models Worcester Bosch C4 14 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