Boiler Fault Code 8.11

Also written as 811 — same fault.

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

Fault code 8.11 appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is not burning gas correctly, which means it may be producing dangerous carbon monoxide and needs to be switched off immediately. (As reported on Chaffoteaux Britony II 30FF)