Boiler Fault Code YELLOW FLAMES / SOOT FORMED

Also written as YELLOWFLAMESSOOTFORMED — same fault.

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

Fault code YELLOW FLAMES / SOOT FORMED appears across 1 boiler brand and 8 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 fuel correctly, which is creating dangerous soot and could potentially release harmful carbon monoxide into your home. (As reported on Chaffoteaux Britony II 50FF)