S.11 Low

Boiler Fault Code S.11

Also written as S11 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code S.11 appears across 3 boiler brands and 57 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 preparing to fire up by starting its internal fan, which is a normal part of the ignition process. (As reported on Vaillant ecoTEC exclusive)

Pick your boiler brand for the S.11 fix

Glow-worm S.11 9 models Heatline S.11 8 models Vaillant S.11 40 models

Source

Information for the S.11 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