D.170 Medium

Vaillant D.170 Fault Code

Also written as D170 — same fault.

The Vaillant D.170 fault code means: your boiler is currently stuck in a specific operational mode while it attempts to communicate with an external control system, meaning it is not responding to your heating or hot water requests.. It appears on 3 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: Hydraulicoperatingmode
Typical repair cost £120-250 (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.170 fault code

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

Source

Vaillant D.170 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