Safety first: Turn off power and gas. Combustion air and flue faults can lead to dangerous operation.

Check flue terminal and intake: Ensure the concentric flue terminal is clear and that the air intake is not obstructed.
Inspect pressure tubes: Open the combustion chamber and locate the silicone tubes between the fan and the air pressure switch. Check for splits, kinks, or blockages (condensate, debris). Replace or clear as needed.
Test air pressure switch: Ensure the electrical connectors are tight. A technician can test the switch with a manometer or continuity meter while the fan runs.
Fan operation: When power is restored and a heat demand is present, listen for the fan starting. If the fan does not run or is noisy, it may be seized or defective and should be replaced.
Professional flue inspection: If E6 persists, have a certified technician inspect the entire flue system and verify correct fan and pressure switch operation.

Furnace locks out with E6, no ignition sequence starts

Possible Causes