BoilerFaultCodes d4:0 Low
Boiler Fault Code d4:0
Also written as D40 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d4:0 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is telling you that the heating system settings are currently turned down to zero, which means it will not provide any heat to your radiators. (As reported on Viessmann Vitodens 333)
Pick your boiler brand for the d4:0 fix
Source
Information for the d4:0 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