Emergency Warning
Burner On neon off on Glow-worm Micron 40FF

Your boiler's burner stays lit even when it should turn off, meaning it isn't responding to your thermostat or timer settings.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description

The burner will remain alight until switched off by the control thermostat, any remote control or the programmer.

What causes this fault?

This fault occurs when the boiler loses its ability to regulate the flame, causing the burner to stay lit regardless of your heating settings. The most common reason is a malfunctioning main circuit board or a faulty gas valve that has become stuck in the open position. It can also be caused by a wiring error in your external thermostat or programmer that is continuously sending a 'heat on' signal.

Engineer required

This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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