BoilerFaultCodesDaikin 1J-64 Fault Code
Also written as 1J64 — same fault.
The Daikin 1J-64 fault code means: your boiler has shut down because it has detected it is getting too hot, often due to low water pressure or poor circulation.. It appears on 1 Daikin model in our database.
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 the Daikin 1J-64 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 →Daikin models that show the 1J-64 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Daikin 1J-64 fault code information on this page is sourced and cross-checked against the official Daikin service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026