High Lockout
neon 4 not lit on Glow-worm Ultimate

Your boiler is failing to light the gas or cannot confirm that a flame is present, meaning the system has shut down for safety.

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

Ignition, pilot or flame proving fault

What causes this fault?

This fault happens when the boiler attempts to start up but cannot successfully ignite the gas or detect a steady flame. It is often caused by a blocked pilot light burner or a worn-out ignition spark, which prevents the main burner from firing up safely. In some cases, the internal control board may also fail to recognise that the flame is lit, prompting the system to shut down for your protection.

This issue often surfaces during the first cold spell of autumn when the boiler is worked harder after being mostly idle throughout the summer.

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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