BoilerFaultCodes Mains On (Green Light) Low
Boiler Fault Code Mains On (Green Light)
Also written as MAINSONGREENLIGHT — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Mains On (Green Light) 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 electrical power and is ready to operate as normal. (As reported on Potterton Promax FSB 30HE)
Pick your boiler brand for the Mains On (Green Light) fix
Source
Information for the Mains On (Green Light) 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