Gas Furnace Troubleshooting

Replace your furnace filters monthly. If you use reusable filters, vacuum the filters monthly.

Brush and vacuum the heat exchanger surface annually.

Check ducts for leaks and wrap with duct tape if any tears are found.

Some fans and fan motors require annual oiling; some do not. Check your owner's manual for details.

Install a carbon monoxide detector near the furnace to alert you in the instance of a carbon monoxide leak.

Some people prefer to do this maintenance themselves. It is recommended that you have a professional perform routine maintenance once a year.

If you have a gas furnace and you smell gas:

Do not try to fix it yourself.

Open windows and get out of the house. Take children and pets with you.

Do not turn on lights or switches.

Call the gas company from a neighbor's house or a cell phone outside the house.

Do not return to the house until a professional has examined your home.

If there's no heat coming from your vents, check the following possibilities:

Check the pilot light to make sure it's lit. You may need to relight it.

Make sure the thermostat is set to "heat". Set the temperature higher than the actual room temperature. This will kick start your gas furnace on and will begin to warm your home. Also check the emergency switch to make sure that it is on.

Check your fuse box to see if any circuit breakers are flipped the wrong way or to make sure a fuse hasn't blown. Reset the circuit breaker or change the fuse if need be.

Make sure the furnace is turned on. Look for the power button.

Reset the blower motor. The motor may have overheated, so wait a few minutes and try resetting it again if the motor does not start up.

Check the thermostat to make sure it is on and is set for at least three degrees hotter than the registered room temperature.

If all these steps don't work, call a professional HVAC technician for a service check.

If heat is coming from the vent, but not enough heat, try the following:

Check the thermostat to make sure it is set to the right temperature.

Check the heating registers - make sure they are open and nothing is obstructing them.

Check the filter. Change it if it's dirty.

If these steps don't help, call a professional HVAC technician and ask him or her to check the blower and the overall system.

If the motor is running, but you can't feel any air moving:

The belt that connects the motor to the blower may be broken.

If you feel confident changing a belt yourself, you can do so (check your manufacturer's specifications in the owner's manual), but call a HVAC technician if you are not comfortable taking this on yourself.

If the furnace keeps cycling on and off repeatedly:

Try cleaning the filter.

Call a technician to see if it's a thermostat or furnace problem.

Watch to see if the room temperature is vacillating significantly. This also indicates a thermostat or heat anticipator problem.

If your furnace blower is constantly blowing air:

Make sure the switch is not on "fan". Switch it to "auto" and see if that fixes the problem.
The limit switch may need adjusting. Your technician can show you how to adjust that.

If the furnace squeals:

A belt that connects the motor to the fan may have slipped or may need to be repaired.

If the furnace is rattling:

Check the registers and make sure the panels are screwed on tight.

Ask your HVAC technician to insert flexible, soft ductwork so the metal ducts won't make so much noise. Metal ducts can be very noisy.

Call a professional if the troubleshooting techniques don't work.