BoilerFaultCodesBaxi On On On Fault Code
Also written as ONONON — same fault.
The Baxi On On On fault code indicates a fault on your boiler. It appears on 2 Baxi models in our database.
Technical description: LV Wiring Harness. Ensure 8-way PCB connector securely pushed in. If fault persists replace LV wiring harness.
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 On On fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi On 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 31 August 2026