BoilerFaultCodesVaillant d.09 Fault Code
Also written as D09 — same fault.
The Vaillant d.09 fault code means: your boiler is simply displaying the target temperature being requested by your external room thermostat or smart control system; this is a status message rather than a breakdown.. It appears on 20 Vaillant models in our database.
Technical description: Heating flow set target temperature that is set on the eBUS room thermostat
DIY fix possible
Check your room thermostat to see if it is calling for heatAdjust your thermostat settings or schedule if the temperature is higher or lower than expectedNo action is required if your heating is performing normally as this is a diagnostic status
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Gas Safe Register →Vaillant models that show the d.09 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT pure
- ecoFIT Pure 412
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 835
- ecoTEC plus
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 65
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus System
- ecoTEC sustain
- Home System
Source
Vaillant d.09 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026