Boiler Fault Code On / Off (Demand fault)

Also written as ONOFFDEMANDFAULT — same fault.

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

Fault code On / Off (Demand 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 receiving a signal to turn on even though your thermostat or timer is not asking for heating or hot water, which may keep the boiler running unnecessarily. (As reported on Worcester Bosch Greenstar i Junior)