D.7 Low

Vaillant D.7 Fault Code

Also written as D7 — same fault.

The Vaillant D.7 fault code means: your boiler is displaying a status message indicating the target temperature for the 'warm start' feature, which keeps water inside the unit pre-heated for faster hot water delivery.. It appears on 6 Vaillant models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Warm start temperature target value

What causes the Vaillant D.7 fault?

This is a normal status code rather than a mechanical failure. It appears when the boiler's internal software is calculating the specific heat level required to keep a small amount of water pre-warmed inside the unit. This ensures that when you turn on a tap, you receive hot water almost instantly rather than waiting for the burner to heat up from cold.

DIY fix possible

Check if the 'C' symbol is displayed on the screen, which indicates warm start is active.Turn the domestic hot water temperature knob fully clockwise to enable or counter-clockwise to disable the feature if preferred.No action is required if your hot water is working normally, as this is an information code rather than a breakdown.

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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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026