Neon 3 lit (No) High

Glow-worm Neon 3 lit (No) Fault Code

Also written as NEON3LITNO — same fault.

The Glow-worm Neon 3 lit (No) fault code means: your boiler has stopped working because it cannot safely clear away waste gases, preventing it from firing up.. It appears on 2 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: Air flow proving fault - that is fan or air pressure switch

What causes the Glow-worm Neon 3 lit (No) fault?

This fault occurs when the boiler's internal safety sensors fail to detect the constant flow of air required to safely expel exhaust gases. The most common cause is a failing fan motor that cannot spin fast enough, or a blocked pressure tube that prevents the system from confirming the fan is working correctly.

This issue can occasionally surface during periods of high winds, as strong gusts can cause back-pressure in the flue that disrupts the sensitive air pressure switch.

Typical repair cost £120-£350 (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 Neon 3 lit (No) fault code

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

Source

Glow-worm Neon 3 lit (No) 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 27 April 2026