High
NEON3 on Glow-worm Micron 40FF

Your boiler has stopped working because it thinks the fan is spinning but it isn't receiving the correct signal to proceed with lighting the burner.

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.

What the manual says

Manufacturer manual

FAN RUNNING

From this model's manual
Verified against the Glow Worm Micron 40ff installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the boiler's internal computer detects that the fan is spinning, but the safety sensor fails to confirm that air is actually moving through the system. The most common reason is a sticking air pressure switch or a fan that has become sluggish due to a build-up of dirt and debris over time. Because the boiler cannot guarantee that harmful exhaust fumes are being safely pushed outside, it shuts down as a safety precaution.

This issue often surfaces during the first cold spell of autumn when a boiler that has been idle over summer is suddenly asked to work at full capacity, causing weakened components like the fan or pressure switch to fail.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Avoid the next call-out bill

A cover plan would handle faults like NEON3: 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.

Related fault codes

Related guides you might find useful