BoilerFaultCodesDaikin J6-01 Fault Code
Also written as J601 — same fault.
The Daikin J6-01 fault code means: your boiler is getting too hot too quickly because water isn't flowing through the system properly or the pressure has dropped too low.. It appears on 1 Daikin model in our database.
Technical description: Flow temperature sensor overheating due to a blocking fault or a lockout error – the valves of the radiator heating circuit may have an issue or the water pressure is low and needs filling
What causes the Daikin J6-01 fault?
This fault occurs when the water inside the boiler heats up much faster than it can be moved away into your radiators. The most common reason is a lack of circulation, often caused by the pump failing, air being trapped in the system, or your radiator valves being closed. It can also be triggered if the system has lost too much water pressure to operate safely.
This fault is frequently seen in autumn when heating systems are turned back on after a long summer break, as pump components can seize during periods of inactivity.
DIY fix possible
Check the pressure gauge and top up the water to 1.5 bar if it is lowEnsure at least two or three radiator valves (TRVs) are fully openRestart the boiler to see if the error clears
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Gas Safe Register →Daikin models that show the J6-01 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Daikin J6-01 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