S.20 Low

Boiler Fault Code S.20

Also written as S20 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code S.20 appears across 3 boiler brands and 59 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is simply letting you know it is currently busy heatng up your hot water tank or keeping its internal water reserve warm. (As reported on Vaillant ecoTEC plus)

Pick your boiler brand for the S.20 fix

Glow-worm S.20 27 models Heatline S.20 2 models Vaillant S.20 30 models

Source

Information for the S.20 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 31 August 2026