Symptoms of a Bad Furnace Heat Exchanger

Cracks

• Over time, the metal in a heat exchanger will start to experience metal fatigue from the constant exposure to severe heat. One of the ways that you should inspect your heat exchanger is to remove the panel that covers the exchanger when the furnace is not operating to check the metal tubes and metal plates. If you see cracks in the metal, the heat exchanger is starting to go bad. You may also want to look for rust spots that are creating openings in the heat-exchanged metal as well.

Open Seams

• Another visual clue that your heat exchanger is going bad is the noticeable separation of the seams in the metal tubes and sheet metal connections. Throughout your heat exchanger are seams where metal plates meet or where the metal tubes were fabricated. Metal fatigue from years of exposure to heat will cause these seams to start to noticeably separate.

Surface Color

• A heat exchanger that can no longer properly contain the heating flame or separate toxic gases will start to show discoloration on the outside of the unit. This discoloration of the edges of the cover of the heat exchanger will be echoed inside the heat exchanger when you remove the cover. The color often looks like areas of dark rust.

Burners

• Carefully watch the flame patterns in your burner as the furnace first turns on its blower to move heat. As the blower motor comes on, the flames in your burner should not react at all. If the flames jump or change color, you could have a damaged heat exchanger.