Boiler Fault Code Frequent sooting (5)

Also written as FREQUENTSOOTING5 — same fault.

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

Fault code Frequent sooting (5) 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 is struggling to burn fuel correctly because the internal parts that manage the gas supply are not the correct size, which is causing dangerous carbon build-up. (As reported on Chaffoteaux Flexiflame 140)