Boiler will not ignite, display shows E01 and burner does not light

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.