Troubleshooting a Gas Furnace Heat Exchanger

The heat exchanger on a gas furnace is responsible for passing the heat from the gas that enters the furnace into the warm air that exits the furnace. The heat exchanger is usually located in the upper part of the furnace and can be difficult to view. If you suspect that there is a leak in the furnace or the furnace is not operating properly, it may be necessary for you to do some troubleshooting.

Flashlight
Telescoping mirror
Stepstool

Instructions

- 1
  Disconnect power to the furnace and open the main access panel.
- 2
  Locate the heat exchanger. Check the surface of the heat exchanger for thinning, rust, soot or condensate leaks.
- 3
  Use a flashlight and a telescoping mirror to look up at the heat exchanger surface inside the furnace. Carefully inspect as much of the heat exchanger as possible.
- 4
  Inspect the seams on the furnace for any signs of cracking or splitting. Check for missing screws or clean-out ports on the heat exchanger.
- 5
  Climb on a stepstool to look inside at the heat exchanger from the opening on the top of the furnace if the furnace is an up-flow system.
- 6
  Restore power to the furnace. Start the furnace by turning the thermostat to “Heat.” Set the thermostat to a temperature above the air temperature. Watch the pilot light carefully as the furnace ignites and starts to burn and the blower fan begins to operate. If the flame jumps, changes color or wavers, the heat exchanger may be damaged.

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