BoilerFaultCodes AL 79 High
Boiler Fault Code AL 79
Also written as AL79 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AL 79 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 has detected an internal electrical fault with the gas control valve, meaning it cannot safely manage the fuel supply and has shut down. (As reported on Sime Dewy 30/130 HE FS)
Pick your boiler brand for the AL 79 fix
Source
Information for the AL 79 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