BoilerFaultCodesBaxi J Fault Code
The Baxi J fault code means: your boiler has detected trapped air in the system or a problem with the temperature sensor, causing it to temporarily pause heating for safety.. It appears on 5 Baxi models in our database.
Technical description: System air / Flow temperature sensor issues
DIY fix possible
Check your system water pressure gauge and top it up to about 1 bar using the filling loop if it is too low.Bleed your radiators starting from the bottom of the house to the top to release any trapped air.Reset your boiler using the reset button to see if the fault clears.
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Baxi models that show the J fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi J fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026