High Lockout
F5 on Glow-worm 30ci Plus

Your boiler has shut down because its internal temperature has risen too high, usually due to a lack of water flow or a circulation blockage.

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

Overheat fault

What causes this fault?

This fault occurs when the water inside the boiler exceeds a safe temperature, triggering a safety shutdown to prevent damage. The most common reason is a failure of the internal pump to move water through the heat exchanger, or a blockage caused by a build-up of debris and sludge within the system.

This fault is more common when the heating is first turned on after summer, as the internal pump can seize up during long periods of inactivity.

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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Related fault codes

F13View →

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