Boiler Fault Code Alarm high limit thermostat

Also written as ALARMHIGHLIMITTHERMOSTAT — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code Alarm high limit thermostat appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that the water inside it has become dangerously hot and has shut down to prevent damage or overheating. (As reported on Vokera Excel)