d.51 Low

Vaillant d.51 Fault Code

Also written as D51 — same fault.

The Vaillant d.51 fault code means: your boiler is currently recalibrating its internal fan settings and is not reporting a failure; it is performing a routine adjustment rather than displaying an active heating breakdown.. It appears on 10 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: Correction of the maximum fan speed: -2500 to 0 rpm. Fan speed=Display value x 10

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.51 fault code

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

Source

Vaillant d.51 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