D.50 Low

Vaillant D.50 Fault Code

Also written as D50 — same fault.

The Vaillant D.50 fault code means: your boiler is notifying you of a minor technical calibration adjustment regarding the fan's lowest operating speed.. It appears on 27 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: Offset for minimum speed

What causes the Vaillant D.50 fault?

This code appears when the boiler's control board detects that the fan is spinning at a slightly different speed than expected during its lowest setting. It is usually caused by natural wear and tear of the fan motor or small electrical inconsistencies between the fan and the main circuit board. While the boiler is correcting itself, it indicates that these components are no longer perfectly synchronised.

Typical repair cost £85-£160 (including labour)

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Vaillant models that show the D.50 fault code

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

Source

Vaillant D.50 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