BoilerFaultCodes AL 03 High
Boiler Fault Code AL 03
Also written as AL03 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AL 03 appears across 1 boiler brand and 12 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 there is too much water pressure in the system, which can cause the safety valves to trigger or the unit to stop working. (As reported on Sime Murelle Pro HE Combi)
Pick your boiler brand for the AL 03 fix
Source
Information for the AL 03 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