Boiler attempts to start but shuts down with E03, fan may run briefly, no ignition noise heard.

Safety: Isolate power to the boiler before inspection. Do not dismantle the flue system unless you are qualified.

• Check flue terminal: From outside, ensure the Atlantic concentric flue terminal is clear of obstructions (ice, leaves, nests). Remove any visible debris without inserting objects into the flue.
• Inspect condensate drain: A blocked condensate trap or pipe can cause backpressure. Check the condensate pipe for kinks, freezing (in cold weather), or blockages. Gently thaw a frozen pipe with warm (not boiling) water.
• Listen for fan operation: On a reset, listen for the fan starting. If the fan is silent or very noisy, it may be seized or failing and requires replacement.
• Professional checks: A technician should test the air pressure switch, verify correct tubing connection, and measure fan speed and pressure differential.