BoilerFaultCodesVaillant D.7 Fault Code
Also written as D7 — same fault.
The Vaillant D.7 fault code means: your boiler is displaying an information code to show that the pre-heated water feature for your taps is currently active.. It appears on 13 Vaillant models in our database.
Technical description: Warm start temperature target value
What causes the Vaillant D.7 fault?
This code appears when the 'Warm Start' feature is turned on, which keeps a small amount of water inside the boiler hot so it reaches your taps faster. It is not a fault, but rather a status message letting you know the unit is briefly firing up to maintain this internal heat. If you see this frequently, it simply means the boiler is keeping itself ready for your next hot shower.
DIY fix possible
Locate the 'Hot Water' dial or button on the control panelTurn the dial slightly clockwise to activate or counter-clockwise to deactivate the pre-heat (Warm Start) functionNo further action is required as this is a status indicator rather than a fault
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Vaillant models that show the D.7 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant D.7 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
- Vaillant ecoMAX 824E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026