D.71 Low

Vaillant D.71 Fault Code

Also written as D71 — same fault.

The Vaillant D.71 fault code means: your boiler is notifying you that its central heating temperature has been set to its maximum possible level.. It appears on 20 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: Maximum setting of heater control knob

What causes the Vaillant D.71 fault?

This code appears when the physical central heating temperature dial on the boiler's control panel has been turned to its maximum position. It is not an internal component failure, but rather the boiler confirming that it is operating at its highest possible heat output. This often happens if someone has bumped the dial or adjusted it manually to try and heat the home faster during a cold spell.

This is more common during the winter months when homeowners increase their thermostat settings or adjust the boiler dial to deal with freezing outdoor temperatures.

DIY fix possible

Locate the heating control knob on the front of the boiler panelTurn the knob slightly to the left to reduce the temperature set-pointCheck if the display returns to the standard pressure or temperature reading

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Vaillant models that show the D.71 fault code

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

Source

Vaillant D.71 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