How much does it cost to fix boiler error code S.25?

Typical repair cost for the boiler S.25 fault is £0-120 including labour.

S.25 Low

Boiler Fault Code S.25

Also written as S25 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code S.25 appears across 4 boiler brands and 49 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is busy prepping for a heating cycle by checking its internal sensors and clearing the flue, but if it stays stuck on this display, it may be failing to light. (As reported on Vaillant ecoTEC plus Regular)

Pick your boiler brand for the S.25 fix

Ariston S.25 5 models Glow-worm S.25 9 models Heatline S.25 8 models Vaillant S.25 27 models

Source

Information for the S.25 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