BoilerFaultCodes Blue light: On / Lockout: Off High
Boiler Fault Code Blue light: On / Lockout: Off
Also written as BLUELIGHTONLOCKOUTOFF — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Blue light: On / Lockout: Off appears across 1 boiler brand and 2 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 request for heating but cannot start the sequence, even though your hot water is still working perfectly. (As reported on Worcester Bosch Greenstar 15i System)
Pick your boiler brand for the Blue light: On / Lockout: Off fix
Source
Information for the Blue light: On / Lockout: Off 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