Clean the heat exchanger

What is going on

Remove the heat exchanger assembly for cleaning. Protect the floor in front of the furnace.

Likely causes

• Soot or scale buildup in the heat exchanger

Check in this order

1. Turn off electrical and gas supply to the furnace.
2. Remove the burner access panel and label, then disconnect gas valve wires.
3. Disconnect the gas supply line from the gas valve.
4. Disconnect the flame sensor wire, ignitor 2-pin plug and rollout switch wires.
5. Remove the four burner assembly screws and remove the gas valve, manifold and burner box as one unit.
6. Clean the burners if needed using the burner cleaning procedure.
7. Remove the condensate trap and the flue collar. Disconnect the condensate drain tubes and the exhaust collar clamps.
8. Disconnect the combustion air inducer, pressure switch wiring and combustion air tubing.
9. Remove the junction box, wiring, primary limit and top cap as needed.
10. Remove the vestibule and heat exchanger assembly from the cabinet.
11. Backwash the heat exchanger with soapy water or steam below 275 °F (135 °C), then rinse and drain it fully.
12. Reinstall all parts in reverse order, making sure the rear baffle sits under the support at the rear of the cabinet.
13. Reconnect gas and electrical supplies, verify connections, then light the furnace and run it for 5 minutes to confirm it is clean and dry.

More furnace guides

• Annual planned service inspection
• Annual service checklist
• Blower access panel and carbon monoxide hazard
• Burner assembly cleaning
• Change blower speed tap
• Check temperature rise and adjust blower speed