Boiler Fault Code S.46

Also written as S46 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026

Fault code S.46 appears across 2 boiler brands and 51 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected very cold temperatures and has automatically turned itself on at a low setting to prevent the internal pipes from freezing. (As reported on Vaillant ecoTEC Plus 620)