BoilerFaultCodes AL 99 High
Boiler Fault Code AL 99
Also written as AL99 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AL 99 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's main internal computer brain has developed a critical fault and is no longer communicating with the rest of the system. (As reported on Sime Murelle EV HE System)
Pick your boiler brand for the AL 99 fix
Source
Information for the AL 99 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 31 August 2026