High Lockout
F4 on Glow-worm Ci Plus

Your boiler is successfully igniting, but it cannot detect the flame and shuts down immediately 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

FAULT: THE BURNER LIGHTS, THEN GOES OUT.

What causes this fault?

This fault occurs when the boiler's safety system fails to confirm that a flame is present even though the burner has physically lit. The most common reason is a buildup of carbon soot on the sensing probe or a loose connection in the wiring that transmits the 'flame detected' signal back to the main control board.

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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