BoilerFaultCodes d.43 Low
Boiler Fault Code d.43
Also written as D43 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d.43 appears across 1 boiler brand and 20 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is notifying you that it is using a specific calculated temperature setting to heat your home, typically when an outdoor weather sensor is connected. (As reported on Vaillant ecoFIT pure)
Pick your boiler brand for the d.43 fix
Source
Information for the d.43 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