BoilerFaultCodesBaxi FLASH ON ON Fault Code
Also written as FLASHONON — same fault.
The Baxi FLASH ON ON fault code means: your boiler's internal computer has developed an electrical fault and is unable to control the heating process.. It appears on 3 Baxi models in our database.
Technical description: Printed circuit board (PCB) fault
What causes the Baxi FLASH ON ON fault?
This fault occurs when the main control board's internal components or solder joints fail due to age, heat stress, or minor electrical surges. Because this part acts as the boiler's brain, any breakdown in its circuitry means it can no longer safely coordinate ignition or monitor safety sensors.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A cover plan would handle faults like FLASH ON ON: no call-out fees, no surprise bills.
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Baxi models that show the FLASH ON ON fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi FLASH ON 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