D.027 Medium

Vaillant D.027 Fault Code

Also written as D027 — same fault.

The Vaillant D.027 fault code means: your boiler has detected an issue with an internal electrical switch module responsible for controlling extra accessories, such as a secondary pump or external heating zone.. It appears on 7 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: Switching of relay 1 on the VR40 "2 in 7" multi-functional module
Typical repair cost £150-250 (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.027 fault code

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

Source

Vaillant D.027 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