How much does it cost to fix boiler error code S.20?

Typical repair cost for the boiler S.20 fault is £60-120 including labour.

S.20 Low

Boiler Fault Code S.20

Also written as S20 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

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 has received a request to provide hot water but is currently unable to complete the cycle, often because it is already cooling down or busy with another task. (As reported on Vaillant ecoTEC 65kW)

Pick your boiler brand for the S.20 fix

Glow-worm S.20 9 models Heatline S.20 8 models Vaillant S.20 42 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 27 April 2026