BoilerFaultCodes AL 42 Medium
Boiler Fault Code AL 42
Also written as AL42 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AL 42 appears across 1 boiler brand and 14 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 one of its control buttons is stuck or faulty, which is preventing you from changing settings or operating the unit properly. (As reported on Sime Murelle Pro HE Combi)
Pick your boiler brand for the AL 42 fix
Source
Information for the AL 42 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