S.15 Low

Boiler Fault Code S.15

Also written as S15 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code S.15 appears across 3 boiler brands and 43 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is performing a self-check to ensure water is moving correctly and the fan is working before it attempts to ignite. (As reported on Vaillant ecoTEC exclusive)

Pick your boiler brand for the S.15 fix

Glow-worm S.15 9 models Heatline S.15 8 models Vaillant S.15 26 models

Source

Information for the S.15 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