BoilerFaultCodes AL 81 High
Boiler Fault Code AL 81
Also written as AL81 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AL 81 appears across 1 boiler brand and 13 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 an issue with the air or gas mixture during ignition, often caused by a blocked chimney or an internal sensor problem, and has shut down for safety. (As reported on Sime Murelle Pro HE System R)
Pick your boiler brand for the AL 81 fix
Source
Information for the AL 81 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