D.47 Low

Vaillant D.47 Fault Code

Also written as D47 — same fault.

The Vaillant D.47 fault code means: your boiler's outside temperature sensor is either giving an incorrect reading or has lost communication with the main control system.. It appears on 26 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: Outside temperature with weather compensator – Vaillant controller only

What causes the Vaillant D.47 fault?

This fault occurs when the boiler loses contact with the sensor located on the outside of your property, which is responsible for monitoring the outdoor temperature. The most common reasons are a break in the communication cable due to weather damage or a internal component failure within the sensor itself. Without this data, the boiler cannot automatically adjust its efficiency based on the weather conditions outside.

This fault is often noticed during the transition into autumn or winter when the heating system's weather compensation features are first called upon after the summer break.

Typical repair cost £100-220 (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.47 fault code

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

Source

Vaillant D.47 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