Boiler locks out and displays F1, burner does not ignite

Safety first: Turn off electrical power to the boiler and isolate the gas supply at the service valve before removing any covers. Only a Gas Safe registered engineer should work on gas-carrying components.

• Reset the boiler: Follow the user manual to perform a reset. If F1 returns repeatedly, continue with checks.
• Check gas supply: Ensure other gas appliances in the property work. If not, contact your gas supplier. Confirm the boiler's gas isolation valve is fully open.
• Inspect flue terminal: From outside, make sure the flue is not blocked by debris, snow, or vegetation, which can affect combustion.
• Check ignition noise: On a call for heat, listen for a clicking sound from the ignition electrode. No clicking may indicate a faulty ignition electrode, lead, or PCB.
• Engineer tasks (do not DIY):
  • Remove the combustion chamber cover and inspect the ignition electrode and flame sensor for cracks, carbon build-up, or incorrect gap. Clean with fine emery cloth and refit or replace as needed.
  • Check the gas valve is receiving the correct voltage from the PCB during ignition and that outlet pressure is within Glow-worm specifications.
  • Verify burner injector and burner head are clean and not partially blocked.

If the fault persists after basic checks, contact a qualified engineer to test combustion, gas valve operation, and ignition components.