Furnace locks out with E03, combustion fan may start but unit shuts down quickly, no ignition.

Safety: Turn off power and gas before inspecting the flue or internal components.

What to check:

• Inspect flue terminal: Go outside and check the Cointra furnace flue terminal for obstructions such as leaves, bird nests, snow, or ice. Clear any blockage carefully.
• Check air intake: If the furnace uses a concentric flue (coaxial), ensure both exhaust and intake paths are clear and not crushed or kinked.
• Examine pressure switch tubing: Open the furnace and locate the silicone tubes running from the combustion fan housing to the air pressure switch. Ensure they are not cracked, kinked, or full of condensate. Replace or drain as needed.
• Test pressure switch operation (basic): With power off, gently blow through the tubing to ensure it is clear. Do not blow into the switch itself. Confirm the electrical connectors are firmly attached.
• Listen to the fan: Restore power and call for heat. Listen for the combustion fan starting. If it hums, squeals, or does not spin, the fan motor may be seized or failing.

Professional service: A qualified technician should measure the pressure switch response, verify correct flue length and configuration per Cointra specifications, and replace the air pressure switch or flue fan if defective. Do not bypass the pressure switch for any reason.