1J-64 High
Your boiler has shut down because it has detected it is getting too hot, often due to low water pressure or poor circulation.
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
Typical repair cost: £100-250 (including labour)
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
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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Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Diverter Valve
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