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

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

S.O Low

Boiler Fault Code S.O

Also written as SO — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code S.O appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is working correctly but is currently in standby because it hasn't received a signal from your thermostat to turn the heating on. (As reported on Vaillant ecoTEC plus VU GB 656/4-5 A)

Pick your boiler brand for the S.O fix

Vaillant S.O 3 models

Source

Information for the S.O 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