D,11 High

Vaillant D,11 Fault Code

Also written as D11 — same fault.

The Vaillant D,11 fault code means: your boiler is struggling to push hot water through your radiators because the external pump that circulates the water is not working correctly.. It appears on 28 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Status external heating pump error

What causes the Vaillant D,11 fault?

This fault occurs when the boiler sends power to the external pump but detects that water isn't moving through the system as expected. The most common reason is that the pump has seized due to a build-up of debris or internal mechanical failure, preventing it from spinning. In some cases, it can also be triggered by a communication error between the boiler's control board and the pump's electrical wiring.

This issue frequently appears at the start of autumn when heating systems are turned back on after being dormant all summer, which can cause the pump to seize.

Typical repair cost £180-£350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the D,11 fault code

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

Source

Vaillant D,11 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