Boiler Fault Code A 20

Also written as A20 — same fault.

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

Fault code A 20 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 has detected heat or fire inside before it has actually allowed any gas through, which is a significant safety protection feature that has now locked the system. (As reported on Vokera Verve I 50)