BoilerFaultCodesBaxi ON OFF ON Fault Code
Also written as ONOFFON — same fault.
The Baxi ON OFF ON fault code means: your boiler has tried to start up several times but failed to light the flame, causing it to shut down for safety.. It appears on 4 Baxi models in our database.
Technical description: Ignition lockout error
What causes the Baxi ON OFF ON fault?
This fault occurs when the boiler's control system attempts to light the burner multiple times but fails to detect a stable flame. The most common reasons include a worn-out ignition spark, a faulty gas valve that isn't opening properly, or an issue with the sensor that confirms the fire is actually lit.
This issue is slightly more frequent in winter as cold weather can affect gas pressure and put older, struggling ignition components under more strain.
DIY fix possible
Check that your gas emergency control valve is open and you have credit on your meterPress the reset button or turn the control knob to 'O' and back to 'I'Check if other gas appliances in your home, like a hob, are working correctly
Find a Gas Safe engineer
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A cover plan would handle faults like ON OFF ON: no call-out fees, no surprise bills.
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Baxi models that show the ON OFF ON fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi ON OFF ON 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 7 July 2026