Boiler Fault Code d.75

Also written as D75 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026

Fault code d.75 appears across 2 boiler brands 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 has taken longer than it should to heat up your hot water cylinder, which usually means the heat isn't being transferred efficiently from the boiler to the tank. (As reported on Vaillant ecoFIT Pure 435)