Boiler Fault Code S.1

Also written as S1 — same fault.

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

Fault code S.1 appears across 1 boiler brand and 26 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber. (As reported on Vaillant ecoTEC plus)