d.14 Medium

Vaillant d.14 Fault Code

Also written as D14 — same fault.

The Vaillant d.14 fault code means: your boiler is struggling to circulate water effectively because the internal pump is not running at the correct speed.. It appears on 20 Vaillant models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Pump speed (ecoMAX 635, 835)

What causes the Vaillant d.14 fault?

This fault occurs when the boiler's control board sends a signal to the internal pump to change speed, but the pump fails to respond or reach the required velocity. The most common reason is that the pump has become seized due to debris in the heating system or the electrical communication cable between the board and the pump has developed a fault.

This issue is more frequent in autumn when the heating is turned back on after a long summer break, as the pump can seize up from lack of movement.

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.14 fault code

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

Source

Vaillant d.14 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 7 July 2026