A faulty or cracked heat exchanger can produce a strong odor similar to the smell of formaldehyde. This odor can cause severe headaches and other symptoms. Have your furnace inspected immediately if you notice a formaldehyde odor in your home.
You should see a blue, steady flame if your gas furnace is working properly. An orange or yellow flame, or a flame that's unsteady and flickering, is a sign that your heat exchanger may be cracked. Call an HVAC technician for heating repairs right away.
Soot Buildup and Discoloration
Soot buildup inside your furnace indicates that it isn't burning cleanly. This is often caused by a cracked heat exchanger. When there are cracks in your heat exchanger, gases will escape. Soot will start to build up and the surrounding metal will become discolored. If you notice unexplained dark spots on your heat exchanger, it's a sign that it has a crack. Call a heating contractor for help as soon as you can.
Carbon Monoxide Alarm
If your heat exchanger is damaged, carbon monoxide can escape through the cracks. Carbon monoxide is dangerous and can even be life-threatening. Make sure you have a carbon monoxide detector on every level of your home. If your carbon monoxide alarm sounds, immediately vacate your home and call your local fire department.