Boiler Fault Code A 18

Also written as A18 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code A 18 appears across 1 boiler brand and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is failing to stay lit because the flame keeps going out shortly after it starts. (As reported on Ariston Euro Combi 30 MFFI)