d.31 Medium

Glow-worm d.31 Fault Code

Also written as D31 — same fault.

The Glow-worm d.31 fault code means: your boiler's automatic system for topping up its internal water pressure is having trouble, which may prevent it from heating your home properly.. It appears on 4 Glow-worm models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Automatic filling device
Typical repair cost £150-250 (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.31 fault code

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

Source

Glow-worm d.31 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