How do you fix a furnace that is blowing black soot?

To troubleshoot and fix a furnace that is blowing black soot, perform basic maintenance tasks, including inspecting the components, vacuuming dust and replacing the filter. If maintenance techniques do not solve the issue, consult a professional.

Soot, a fine black powder, is often a sign of poor combustion. To perform maintenance tasks to possibly resolve the issue:

1. Turn off the power and remove covers
Turn the power off at the electrical power switch, then remove the combustion chamber door and burner cover, which may be attached with two screws.
2. Inspect the flames
Turn the power switch back on and turn up the thermostat to ignite the flames. They should be even and blue. Dirty burners can cause yellow flames. Call a professional to adjust the flames if necessary.
3. Vacuum
Turn the power switch off again, then shut off the gas with a one-quarter turn of the valve. Vacuum out all areas, including the blower compartment. Inspect for soot and note where it is located.
4. Remove the blower
Remove the two screws attached to the blower, then remove the two bolts holding it in place. Then, carefully remove it.
5. Clean the blower blades
Use a vacuum and brush to carefully clean the blades, taking care not to disturb the blade counterweights. Thoroughly clean all areas so as not to throw it off balance.
6. Change the filter
Replace the furnace's filter.
7. Consult a professional
There are many regular maintenance tasks to perform on furnaces, and if they do not solve the issue, it is time to consult a professional.