E04
Baxi
Flame Detection Fault / Ionisation Failure
Boiler displays E04, no ignition, may attempt to start then lock out
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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
Contaminated or damaged flame sensing electrode, Poor earth connection on boiler chassis, Faulty Baxi PCB flame detection circuit, Incorrect gas/air mixture at burner
How to Fix / Troubleshooting
Safety first: Flame sensing is part of the safety chain. Do not bypass or tamper with sensors.
User checks:
- Perform a single reset and observe whether the boiler lights and stays on.
- Ensure the boiler casing is correctly fitted and not distorted, as poor earthing can affect flame sensing.
- Check for stable mains power (no frequent brownouts or flickering lights).
Professional actions:
- A Gas Safe engineer should inspect and clean the flame sensing electrode, check the earth continuity, and verify burner condition.
- If necessary, they will test the PCB flame detection circuit and gas valve settings.
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Repair Difficulty
Professional Required
5/5
Required Part
Flame Sensing Electrode
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