d.34 High

Glow-worm d.34 Fault Code

Also written as D34 — same fault.

The Glow-worm d.34 fault code means: your boiler has detected that the internal fan responsible for venting exhaust gases is not spinning at the correct speed, so it has shut down to keep you safe.. It appears on 6 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: Speed of fan
Typical repair cost £180-350 (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 →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like d.34: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Glow-worm models that show the d.34 fault code

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

Source

Glow-worm d.34 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