Controller shows E3 and burner does not start, fan may run briefly then stop

Safety first: Disconnect power before removing any covers. Do not operate the furnace with the flue or intake disconnected.

Steps:

• Inspect venting: Check the flue pipe and combustion air intake for obstructions, sagging, or disconnections. Remove any debris and ensure proper slope and support as per installation manual.
• Check pressure tubing: Locate the air pressure switch connected to the Danfoss control. Inspect the silicone or rubber tubes for cracks, kinks, or water accumulation. Re-seat or replace tubing as needed.
• Test pressure switch operation (basic): With power off, gently blow through the tubing to ensure it is clear. With power on and a call for heat, listen for the induced draft fan starting. You may hear a faint click from the pressure switch when the fan runs. No click may indicate a faulty switch or fan.
• Verify induced draft fan: Check that the induced draft fan wheel spins freely by hand (power off). Look for signs of seized bearings or foreign objects. If the fan does not run during a call for heat, the fan motor or its capacitor may be defective.
• Reset and test: After clearing obstructions and securing tubing, reset the controller. If E3 persists, the pressure switch or fan assembly likely needs replacement by a technician.