Boiler Fault Code D.009

Also written as D009 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code D.009 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 receiving a signal from your thermostat or controller, and this code is simply telling you that it is currently processing an instruction to adjust your heating temperature. (As reported on Vaillant ecoTEC Pro 30)