BoilerFaultCodes D.90 Low
Boiler Fault Code D.90
Also written as D90 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.90 appears across 1 boiler brand and 5 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 waiting for a signal from an external smart control or thermostat, meaning it is in a standby or communication phase rather than a fault. (As reported on Vaillant ecoTEC plus Regular)
Pick your boiler brand for the D.90 fix
Source
Information for the D.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