Boiler Fault Code A 0 3

Also written as A03 — same fault.

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

Fault code A 0 3 appears across 1 boiler brand and 1 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 waste gases are not being cleared away safely and has automatically shut down to prevent a build-up of fumes. (As reported on Ferroli Arena 30 C)