Furnace shows E05 and will not complete ignition sequence; inducer may start and stop repeatedly

Safety first: Turn off power and gas. Condensate components may contain acidic water; wear gloves and eye protection.

• Check condensate drain: On high-efficiency Napoleon furnaces, locate the condensate trap and PVC drain line. Remove the trap and flush it with warm water to clear sludge or debris. Ensure the drain line to the floor drain or pump is not kinked or blocked.
• Inspect pressure tubing and ports: Remove tubing from the pressure switch and inducer/collector box ports. Use a small drill bit or paper clip (by hand only) to gently clear any debris from the ports. Reattach tubing securely.
• Test inducer strength: Restore power and call for heat. Confirm the inducer starts promptly and runs at full speed. A noisy or slow inducer may not create enough vacuum to close the pressure switch.
• When to replace: If the condensate system is clear and the inducer runs strongly but the pressure switch does not close (verified with a multimeter), replace the pressure switch with the correct Napoleon part. If the inducer is weak or seized, replace the inducer assembly.