BoilerFaultCodes S.90 Low
Boiler Fault Code S.90
Also written as S90 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code S.90 appears across 1 boiler brand and 8 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is currently performing a mandatory internal self-check sequence and is not indicating a fault. (As reported on Heatline Capriz Plus)
Pick your boiler brand for the S.90 fix
Source
Information for the S.90 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