BoilerFaultCodesBaxi ON OFF FLASH Fault Code
Also written as ONOFFFLASH — same fault.
The Baxi ON OFF FLASH fault code means: your boiler has detected that the electrical wiring coming into the unit is connected the wrong way around, causing it to shut down for safety.. It appears on 1 Baxi model in our database.
Technical description: Live and neutral reversed error
What causes the Baxi ON OFF FLASH fault?
This fault occurs when the electrical supply to the boiler has been wired incorrectly, meaning the electricity is flowing in the opposite direction than intended. It most commonly happens after recent electrical work in the home or if a new plug socket has been installed incorrectly near the heating system.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Baxi models that show the ON OFF FLASH fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi ON OFF FLASH 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