BoilerFaultCodes d.09 Low
Boiler Fault Code d.09
Also written as D09 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d.09 appears across 3 boiler brands and 23 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 an instruction from an external heating control, such as a smart thermostat or weather sensor, and is simply confirming that it is operating according to those settings. (As reported on Heatline Capriz Plus)
Pick your boiler brand for the d.09 fix
Source
Information for the d.09 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 7 July 2026