d.34 Low

Vaillant d.34 Fault Code

Also written as D34 — same fault.

The Vaillant d.34 fault code means: your boiler is displaying the current fan speed for diagnostic purposes rather than an error, but it may indicate an issue with how the fan is communicating with the 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: Value for the fan speed
Typical repair cost £180-450 (including labour)

DIY fix possible

Navigate the digital display to your main screenNo action is required as this is a diagnostic statusIf the boiler is not firing, try a single resetMonitor for actual error codes like F.32

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Vaillant models that show the d.34 fault code

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

Source

Vaillant d.34 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 31 August 2026