Furnace locks out with F1 displayed, burner does not ignite

Safety first: Turn off electrical power to the furnace 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 and combustion settings.

Basic checks a homeowner can do:

• Reset the appliance using the front panel reset procedure (refer to the user manual). If F1 returns repeatedly, do not keep resetting.
• Check that the gas supply to the property is available (other gas appliances working, meter not locked off).
• Ensure the condensate pipe is not frozen or blocked, as this can sometimes cause ignition issues.

Technical checks (for a qualified technician):

• Remove the combustion chamber cover and visually inspect the ignition electrode and lead for cracks, carbon tracking, or damage. Clean light deposits with a non-metallic abrasive pad.
• Check the electrode gap and position relative to the burner as per the Glow-worm service manual for the specific model.
• Verify continuity of the ignition lead from the electrode to the ignition transformer/PCB.
• Check burner earth connection and main earth continuity to the chassis.
• Confirm correct gas inlet pressure and that the gas valve is opening during ignition sequence.
• If all mechanical and wiring checks are satisfactory, test the ignition circuit on the main PCB and replace the control board if out of specification.