BoilerFaultCodesDaikin JJ-64 Fault Code
Also written as JJ64 — same fault.
The Daikin JJ-64 fault code means: your boiler is not receiving enough electrical power from your home's mains supply to operate safely.. It appears on 1 Daikin model in our database.
Technical description: Supply voltage is below low limit
What causes the Daikin JJ-64 fault?
This fault occurs when the electrical supply entering your boiler drops below the minimum level required for its internal components to function correctly. It is often caused by instability in the local power grid, a faulty electrical connection within your home, or a failing internal control board that can no longer process the incoming voltage.
This issue can be more frequent during periods of extreme cold or heatwaves when the national grid is under heavy load, potentially causing 'brownouts' or voltage fluctuations in residential areas.
DIY fix possible
Check if there is a power cut or brownout in your local areaEnsure your fuse box / consumer unit has not trippedTurn the boiler off at the fused spur switch, wait 30 seconds, and turn it back on to reset the electronics
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Daikin models that show the JJ-64 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Daikin JJ-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