Lockout lamp illuminating (Overheat Thermostat) High

Boiler Fault Code Lockout lamp illuminating (Overheat Thermostat)

Also written as LOCKOUTLAMPILLUMINATINGOVERHEATTHERMOSTAT — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code Lockout lamp illuminating (Overheat Thermostat) 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 switched itself off to prevent damage because the unit has become too hot. (As reported on Malvern TenTwenty)

Pick your boiler brand for the Lockout lamp illuminating (Overheat Thermostat) fix

Malvern Lockout lamp illuminating (Overheat Thermostat) 1 model

Source

Information for the Lockout lamp illuminating (Overheat Thermostat) 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 7 July 2026