BoilerFaultCodes D.091 Low
Boiler Fault Code D.091
Also written as D091 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.091 appears across 1 boiler brand and 7 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 trying to synchronize its internal clock with a radio signal from a time transmitter, which is a standard background process and not a system fault. (As reported on Vaillant ecoTEC Pro 28)
Pick your boiler brand for the D.091 fix
Source
Information for the D.091 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 7 July 2026