Boiler Fault Code On / Off (HW fault)

Also written as ONOFFHWFAULT — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code On / Off (HW fault) 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 heating the radiators normally, but it is failing to switch over to provide hot water to your taps. (As reported on Worcester Bosch Greenstar i Junior)