BoilerFaultCodes ALARM 04 Medium
Boiler Fault Code ALARM 04
Also written as ALARM04 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code ALARM 04 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 a fault with the domestic hot water sensor, meaning it may still provide heating but cannot accurately control the temperature of your hot water. (As reported on Sime Murelle HE System)
Pick your boiler brand for the ALARM 04 fix
Source
Information for the ALARM 04 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