High Lockout
Neon 4 NOT lit on Glow-worm Space Saver Compleheat 30 40 50

Your boiler is failing to light the pilot flame or detect a steady flame, meaning it cannot start the heating process.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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 occurs when the boiler attempts to start up but cannot establish or maintain the small pilot flame needed to ignite the main burner. The most common reasons are a blocked pilot hole preventing gas flow or a worn-out sensor that can no longer tell the boiler it is safe to stay on. In some cases, the gas valve may be failing to release the fuel required to start the ignition process.

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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