CO Low

Boiler Fault Code CO

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code CO appears across 1 boiler brand and 8 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is currently running in a special engineer-only testing mode for checking gas emissions and is not experiencing a mechanical fault. (As reported on Vokera Syntesi E)

Pick your boiler brand for the CO fix

Vokera CO 8 models

Source

Information for the CO 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