Boiler Fault Code A 18

Also written as A18 — same fault.

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

Fault code A 18 appears across 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is struggling to confirm that the flame has turned off properly after it finished its heating cycle, which is a safety mechanism to prevent gas buildup. (As reported on Vokera Verve I 50)