BoilerFaultCodes Mains light off High
Boiler Fault Code Mains light off
Also written as MAINSLIGHTOFF — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Mains light off 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 has lost all electrical power, meaning it cannot provide any heating or hot water until the power supply is restored. (As reported on Ideal Concord Super Series 4)
Pick your boiler brand for the Mains light off fix
Source
Information for the Mains light 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