E01
Main
Ignition Lockout
Boiler will not ignite, display shows E01 and burner does not light
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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
Faulty ignition electrode, Damaged ignition lead, Gas valve not opening, Flame sensing (ionisation) fault
How to Fix / Troubleshooting
Safety first: Turn off electrical power to the boiler at the isolator and close the gas isolation valve before removing any covers. Only a Gas Safe registered engineer should work on gas-carrying components.
- Reset the boiler: Refer to the Main boiler user manual and perform a reset using the front panel reset button. Observe if E01 reappears.
- Check gas supply: Ensure other gas appliances (e.g. hob) work. If not, contact your gas supplier. Confirm the boiler gas isolation valve is fully open.
- Inspect flue terminal: From outside, ensure the flue is not blocked by debris, snow, or vegetation, which can affect combustion.
- Visual check through sight glass: When power is restored and a demand for heat is present, observe whether a spark is visible at the burner (do not remove the sealed combustion cover unless qualified). No spark suggests an ignition electrode/lead or PCB issue.
- Engineer checks (Gas Safe only):
- Test and clean the ignition electrode and ionisation probe on the Main burner assembly; check gap and ceramic insulation.
- Check continuity and insulation of the ignition lead between PCB and electrode.
- Measure gas valve coil resistance and verify correct operation and supply from the Main control PCB.
- Verify correct gas inlet pressure and burner pressure according to Main boiler specifications.
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Repair Difficulty
Professional Required
5/5
Required Part
Ignition Electrode and Lead
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