S.04 Low

Boiler Fault Code S.04

Also written as S04 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code S.04 appears across 4 boiler brands and 65 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is operating normally and is currently heating up to provide warmth or hot water. (As reported on Glow-worm Ultracom 2 SXI)

Pick your boiler brand for the S.04 fix

Ariston S.04 5 models Glow-worm S.04 12 models Heatline S.04 8 models Vaillant S.04 40 models

Source

Information for the S.04 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