High Lockout
Neon 2 NOT lit on Glow-worm Glow-worm Micron 100FF 120FF

Your boiler has stopped running because it has either detected that it is getting too hot or the water pressure in the system has dropped too low.

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

Low water pressure (sealed system), Overheat cut off device tripped or thermostat, overheat cut off device faulty

What causes this fault?

This fault occurs when the water inside the boiler exceeds a safe operating temperature or if there isn't enough water circulating to carry heat away. The most common reasons are a build-up of sludge blocking the heat exchanger, a failing pump, or a simple loss of pressure in the central heating pipes.

This issue often appears when the heating is first turned on in autumn, as pumps can seize after being inactive during the summer months.

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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