BoilerFaultCodesDaikin HJ-09 Fault Code
Also written as HJ09 — same fault.
The Daikin HJ-09 fault code means: your boiler has detected that the water pressure is too low to operate safely, causing it to shut down temporarily.. It appears on 1 Daikin model in our database.
Technical description: Low system pressure – increase the system pressure to 0.8 bar
What causes the Daikin HJ-09 fault?
This fault occurs because the internal sensors have detected that there is not enough water inside the central heating system to circulate safely. The most common reason is a minor leak in the pipework or radiators, though it can also happen if air was recently bled from your radiators without the pressure being topped up.
This issue is frequently seen at the start of autumn when homeowners turn their heating back on for the first time after the summer break.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the one or two taps/levers on the filling loop until you hear water moving.Watch the pressure gauge and close the taps firmly once the needle reaches 1.5 bar.
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Gas Safe Register →Daikin models that show the HJ-09 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Daikin HJ-09 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