How much does it cost to fix boiler error code C18?

Typical repair cost for the boiler C18 fault is £150-250 including labour.

C18 High

Boiler Fault Code C18

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code C18 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is struggling to detect the flow of water because a sensor is failing, which means it has stopped heating your home or water to prevent internal damage. (As reported on Atag Premier)

Pick your boiler brand for the C18 fix

Atag C18 1 model

Source

Information for the C18 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