D.35 Low

Vaillant D.35 Fault Code

Also written as D35 — same fault.

The Vaillant D.35 fault code means: your boiler is currently switching over between its heating and hot water functions.. It appears on 21 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: Not relevant

What causes the Vaillant D.35 fault?

This status occurs when the internal diverter valve physically moves to switch the flow of heated water between your radiators and your hot water taps. It is a normal mechanical process where the boiler pauses momentarily to ensure heat is directed to the right place. You will see this on the screen briefly during transitions, such as right after you turn off a hot tap while the heating is on.

DIY fix possible

No action is required as this is a normal status message rather than a fault.Wait a few moments for the boiler to complete its cycle.If the boiler appears stuck, try a simple reset by pressing the flame button.

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Vaillant models that show the D.35 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant D.35 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