d.51 High

Glow-worm d.51 Fault Code

Also written as D51 — same fault.

The Glow-worm d.51 fault code means: your boiler is struggling to correctly adjust the speed of the internal fan that clears exhaust gases, which is preventing it from starting up properly.. It appears on 7 Glow-worm models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Correction of the maximum fan speed
Typical repair cost £150-300 (including labour)

Engineer required

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

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Glow-worm models that show the d.51 fault code

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

Source

Glow-worm d.51 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026