BoilerFaultCodes S.09 Low
Boiler Fault Code S.09
Also written as S09 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code S.09 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 currently performing a routine self-check to ensure it is burning fuel efficiently, and this usually only lasts for a few moments. (As reported on Vaillant ecoTEC exclusive)
Pick your boiler brand for the S.09 fix
Source
Information for the S.09 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026