Boiler displays E03 and shuts down, fan may start briefly then stop, no ignition attempt.

Critical safety warning: E03 can indicate a flue gas evacuation problem. Risk of carbon monoxide. Turn off the boiler and do not attempt to run it until the flue system has been checked by a qualified technician.

User checks (external only):

• Visually inspect the outside flue terminal for obstructions such as leaves, nests, snow, or debris. Do not dismantle the flue.
• Ensure ventilation grilles in the boiler room are not blocked.
• Reset the boiler once after clearing any obvious obstruction. If E03 returns, stop and call a professional.

Technician checks:

• Inspect the entire coaxial flue system for blockage, incorrect slope, or water accumulation; rectify or replace components as needed.
• Test the flue gas thermostat / flue NTC sensor mounted on the flue hood or heat exchanger; replace if open circuit or out of range.
• Check operation of the fan assembly (Termet OEM fan) including speed feedback to the main PCB.
• Verify combustion parameters with a flue gas analyser and adjust the gas valve if necessary.

Do not bypass or short any flue safety devices. Only an authorised Termet service engineer should work on the flue and combustion system.