High
Neon 4 NOT lit on Glow-worm Glow-worm Micron 100FF 120FF

Your boiler is trying to start up but cannot light the small pilot flame needed to ignite the main heating system.

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

Ignition, pilot or flame proving fault

From this model's manual
Verified against the Ultimate 100ff 120ff 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 safety system fails to detect a constant flame after several attempts to spark. The most common reasons are a blocked pilot jet preventing gas flow, a worn-out ignition lead that can no longer create a spark, or a faulty sensor that cannot confirm the flame is actually lit.

This issue often surfaces after a long summer break when debris or spiders' webs have settled in the pilot tube, blocking the small amount of gas needed for ignition.

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.

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