BoilerFaultCodes d.04 Low
Boiler Fault Code d.04
Also written as D04 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d.04 appears across 1 boiler brand and 22 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is displaying the current temperature of the water inside your hot water storage cylinder; this is a status information code rather than a system failure. (As reported on Vaillant ecoFIT Pure 435)
Pick your boiler brand for the d.04 fix
Source
Information for the d.04 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