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If your furnace goes out unexpectedly, try the following furnace troubleshooting tips before reaching for the phone. You may be able to fix the problem yourself.

Top 7 Common Furnace Problems & How to Fix Them

If your furnace isn’t working properly, it could be a simple fix. Here are five common furnace problems that homeowners can address themselves to figure out why their furnace isn’t working:

1. The Thermostat

The first thing to check to figure out why your furnace isn’t working is the thermostat. Verify the following:

• The thermostat is set to heat, and the temperature is set above the air temperature by a few degrees. If in doubt, set the temperature four degrees higher.
• If there is no response or the display screen is blank, try replacing the batteries in the thermostat if it isn’t hard-wired. If it is hard-wired, check its circuit breaker.
• Remove any dust on the thermostat, which may clog its sensors and prevent accurate readings.
• Ensure your thermostat has the right time and settings. It may be on a “run” cycle, and the time may be set to an “inactive” period.

If everything with your thermostat seems to be in check, there is likely another issue that is causing your furnace not to work.

2. No Power

All gas furnaces have a switch located in front of the blower compartment. Reset it by pushing it to the “On” position.

If that doesn’t do the trick, check if the circuit breaker tripped. If any of the breaker switches are partially or wholly flipped in another direction from the rest of them, it means it has tripped. Flip the switch fully to the “Off” position (away from the others), then flip it to the “On” position to line it up with the others.

If the breaker trips soon after resetting it, call your HVAC contractor for professional help.

3. Low Air Flow or Limited Heat

Most furnaces have safety switches inside them that automatically turn off if there isn’t enough airflow. Sometimes, if a filter is left for too long and is covered in dust, it won’t allow enough air into the blower compartment, and the safety switch will flip.

Allowing the unit to run without the safety switch could be a safety hazard as the dust buildup can cause a heat buildup, which could result in a fire. During the cold months, you should check your air filter monthly to ensure it is clean.

If your filter is dirty, replace it with a new one.

4. Furnace Does Not Blow Air

Look into the inspection window on the furnace and check to ensure the blower is free of any debris. Ensure there are no obstructions to the blower or ductwork.

Check your return vent and ensure that there is free airflow. Return vents should not be covered by furniture or carpet. For best airflow, ensure there is at least 12 inches of room around the return vent.

5. Ignition Problems

Diagnosing furnace ignition problems is fairly easy with a furnace that uses a standing pilot light. If the pilot goes out periodically, clean the thermocouple and the pilot. If the pilot still goes out, the thermocouple may need replacing.

If your furnace has electronic ignition, it uses a furnace ignitor. This part uses a filament that creates a spark to ignite the fuel. They can and do wear out, and should be replaced by an HVAC professional.

6. Noisy Furnace or Ductwork

While your furnace will make some noise when it first gets going, it shouldn’t make loud noises like rumbling, squeaking, and rattling. If the noises are very odd, it could be that your pilot light is improperly adjusted or the blower motor needs lubrication. There could also be problems with the belts or the burner.

Here are some different sounds to look out for:

• Pinging or Popping: Pinging and popping sounds are usually due to thermal expansion, which is the ductwork expanding and contracting as it heats and cools. If the sounds are from the furnace itself, it could be the heat exchanger.
• Rattling: You may have some loose panels or ductwork that needs tightening.
• Squealing: This is often a belt that connects to the motor that slipped off or broke. The belt will need to be replaced.
• Grinding: Grinding sounds usually mean the motor bearings need to be replaced. Replacing bearings to repair your furnace will require a professional HVAC technician.

7. Clear Intake & Exhaust Vents

If your furnace has vents going out of the side of the house, it’s important to make sure nothing is blocking them. They need clear access to the air. Clear away grass, bushes, leaves, and other obstructions away from the vents. Both gas furnaces and heat pumps will have exhaust vents, though they aren’t always on the side of the house—they may go through the roof instead.

Apollo Home is Cincinnati’s premier HVAC contractor. If you are having heating system problems, contact Apollo Home. We offer expert furnace, heat pump, and heating system repairs and replacements in Cincinnati, Northern Kentucky, and Dayton, Ohio.