BoilerFaultCodesYour boiler has shut down because it has detected it is getting too hot, often due to low water pressure or poor circulation.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: High limit thermostat signalising overheating. Check the valve of the radiators in the heating, check if the Combi boiler water pressure is low, if it is then the heating circuit needs filling with water
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to shut the system down to prevent damage. The most common reasons are a lack of water pressure to move heat away from the burner, or a mechanical blockage like a stuck pump or closed radiator valves preventing the water from circulating.
This issue is frequently seen in autumn when the heating is turned on for the first time after summer, as pump components can seize during long periods of inactivity.
DIY fix possible
Check the pressure gauge and top up the water to between 1 and 1.5 bar if it is lowEnsure at least two or three radiator valves are fully open to allow water to flowRestart the boiler using the reset button to see if the fault clears
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like 1J-64 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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