E02
Baxi
Primary Heat Exchanger Overheat / Safety Thermostat Trip
Boiler locks out with E02, overheats and shuts down, may make kettling noises before stopping
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blocked or scaled Baxi primary heat exchanger, Failed overheat thermostat or NTC sensor, Pump not circulating water through boiler, Airlock or closed isolation valves on flow/return
How to Fix / Troubleshooting
Safety first: Switch off the boiler at the fused spur and allow it to cool fully before touching any pipework. Do not remove the combustion cover.
User checks:
- Check that all radiator valves and any isolation valves under the boiler (flow and return) are fully open.
- Verify system pressure is around 1.0–1.5 bar when cold. Re-pressurise via the filling loop if needed, following the Baxi instructions.
- Bleed radiators to remove trapped air, starting with the highest radiators. Top up pressure again afterwards.
- Press the reset button once and observe whether the boiler runs without quickly overheating.
If kettling or rapid overheating persists:
- Do not continue resetting the boiler repeatedly; this can stress components.
- Limescale or sludge may be restricting flow through the primary heat exchanger or system pipework.
- A Gas Safe engineer should check pump operation, clean or chemically flush the system, and test/replace the overheat thermostat and NTC sensors if required.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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