Boiler Fault Code AL 15

Also written as AL15 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code AL 15 appears across 1 boiler brand and 19 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 the internal fan responsible for venting exhaust gases is not spinning at the correct speed, so it has safely shut itself down to prevent unsafe operation. (As reported on Sime Format DGT HE System)