About The Author: Travis Baugh is a Digital Brand Marketing Manager for Bryant, where he creates clear, helpful content to guide homeowners through heating, cooling, and indoor air quality decisions. His goal is to empower readers with the knowledge they need to choose the right comfort solutions for their home—confidently and comfortably.
Furnace Troubleshooting: A Comprehensive Guide to Common Fixes
Furnace troubleshooting is the process of inspecting your heating system's core components—such as the thermostat, air filter, and power supply—to identify why it isn't heating. Common issues often stem from simple oversights like incorrect settings or clogged airflow. By addressing these basics, you can often restore your home's comfort and avoid a service call.
How do I troubleshoot my furnace?
To troubleshoot a gas furnace, follow these four steps:
- Check the thermostat: Ensure it is set to "Heat" and the temperature is set higher than the room temperature.
- Inspect the air filter: Replace the filter if it is gray or clogged with debris to restore airflow.
- Verify power: Check that the furnace switch is "On" and no circuit breakers are tripped.
- Clear vents: Confirm that all supply and return vents are open and unobstructed by furniture or rugs.
1. Is the Thermostat Set Correctly?
The most common reason a furnace won't turn on is a simple thermostat setting error. Before investigating mechanical components, verify your control panel.
- Mode Selection: Verify the thermostat is set to "Heat." If it was accidentally bumped to "Off" or "Cool," the furnace won't engage.
- Power Source: If the display is blank, check the batteries. Many digital thermostats require fresh batteries to operate the relay that signals the furnace.
- Calibration: If the room feels colder than the setting, the thermostat may need recalibration. Consult your user manual to ensure it is reading the room temperature accurately.
2. Is the Furnace Filter Dirty or Clogged?
A dirty filter is a leading cause of furnace malfunctions. When a filter becomes clogged with dust and debris, it restricts airflow, causing the system to overheat and shut down (a safety mechanism called "short cycling").
- Check the size: Locate the size printed on the side of your current filter (e.g., 16x20x1).
- Inspect condition: Slide the filter out. If it looks gray and fuzzy with dust, it needs replacing.
- Replacement schedule: Generally, replace standard 1-inch filters every 1–3 months. Homes with pets may need more frequent changes. Learn more about replacing the furnace filter.
"The most important thing replacing the furnace filter does is improve indoor air quality," Mike Lea, co-owner of Lea Heating & Air Conditioning in East Dundee, IL said. "It also keeps your HVAC system running at top efficiency, helps lower heating bills, helps prevent costly breakdowns and furnace service calls, and helps extend the lifespan for your furnace. What happens is that the clogged air filter makes the system work harder, which puts more strain on the blower motor and causes the heat exchanger to overheat. It's probably our number one most frequent service call in the winter when the furnaces is short cycling. It's generally from a dirty air filter or using too restrictive of an air filter."
3. Does the Furnace Have Electrical Power?
If your natural gas furnace isn't turning on at all, it may have lost electrical power. Even gas furnaces need electricity to run the blower motor and ignition system.
- Furnace Switch: Look for a standard light switch on the side of the furnace or a nearby wall. Ensure it is flipped "Up" or "On."
- Circuit Breaker: Go to your home's electrical panel. Look for the breaker labeled "Furnace" or "HVAC." If it is in the middle or "Off" position, flip it fully off and then back on to reset it.
- Fuse Box: If you have an older fuse box, check for a blown fuse and replace it with one of the same amperage.
4. Are Vents and Ducts Blocked?
For your home to heat evenly, air must flow freely through the supply vents (where heat comes out) and return vents (where air goes back to the furnace).
- Check all rooms: Walk through your home and ensure furniture, curtains, or rugs aren't covering the registers.
- Open dampers: Make sure the levers on the vent covers are in the open position.
Restricted airflow forces your system to work harder, increasing energy bills and wear on components. Regular furnace maintenance and furnace cleaning can help keep your ductwork clear.
When to Call a Professional
If you have completed these four steps and the furnace still won't run, contact a professional immediately. Complex issues involving the igniter, flame sensor, or blower motor require specialized diagnostic tools.
Andrew Mackey, owner of Superior Service in Lake St Louis, Missouri, warns against customers trying to do too much furnace troubleshooting on their own.
“We recommend the homeowner to call a qualified and licensed contractor to troubleshoot a furnace,” Mackey said. “The only thing a homeowner should be doing is changing the filter on a normal basis.”
Connect With A Bryant Dealer For Further Furnace Troubleshooting
If your furnace still isn't performing as expected after performing these steps, connect with a Bryant dealer for expert troubleshooting and diagnostics. Their trained technicians can identify the root cause of the issue—whether it’s a mechanical failure, thermostat problem, or airflow restriction—and recommend the right solution. Prompt furnace service from your local Bryant dealer helps prevent further damage and ensures reliable, efficient operation. Schedule an appointment for furnace repair or furnace replacement today.
Furnace Troubleshooting FAQs
Start by checking the thermostat settings, circuit breakers, air filter, and pilot light or ignition system—if the issue isn’t obvious, it’s best to call a licensed HVAC technician for diagnosis.
The most common early failures are the igniter or flame sensor, as they experience regular wear and tear and are critical to starting the heating cycle.
Keep the area clear, replace filters regularly, and install carbon monoxide detectors near sleeping areas.
If the unit won’t turn on and no indicator lights show, check the fuse box or circuit board for a blown fuse and replace it if necessary.
Learn More About Furnaces
- Read our guide to furnace parts
- Learn how much is a new furnace
- Get help with a furnace not turning on or a furnace leaking water
- Find out how long does a furnace last
- Find out how to fix a furnace blowing cold air
- Understand the ins and outs of a furnace tune-up
