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.
Why Is My Furnace Not Turning On?
By Travis Baugh
If your furnace is not turning on, it's often due to a simple issue like incorrect thermostat settings, a tripped circuit breaker, or a dirty air filter. These problems can prevent the furnace from receiving power or cause it to shut down as a safety measure, leaving your home cold.
When the temperature drops, a furnace that won't start can be stressful. Understanding the common causes can help you troubleshoot the problem and restore warmth to your home efficiently. This guide covers the most frequent reasons a furnace is not working and provides a step-by-step checklist to resolve the issue.
What Are the Most Common Reasons a Furnace Is Not Working?
If your furnace isn’t turning on, it can be due to a variety of issues.
Andrew Mackey, owner of Superior Service in Lake St. Louis, Missouri, explains the most common reasons a furnace may not turn on.
“It could be as simple as a tripped breaker,” Mackey said. “The unit might also shut off if the filter is too dirty, or another common cause is a dirty flame sensor.”
Here are 12 common causes to investigate::
- Thermostat Issues: The problem could be as simple as dead batteries, incorrect settings (not set to "heat"), or a complete thermostat malfunction.
- Tripped Circuit Breaker: Your furnace requires electricity to run. If its circuit breaker has tripped, the system has no power.
- Blown Fuse: Some older furnaces have an internal fuse that can blow, cutting off power and preventing operation.
- Ignition or Pilot Light Problems: On older models, the pilot light may have gone out. On modern furnaces, a faulty electronic igniter or gas valve can prevent it from starting.
- Dirty Air Filter: A clogged furnace filter is a primary cause of a furnace not working. It restricts airflow, which can cause the system to overheat and shut down.
- Gas Supply Issues: The gas valve to your furnace may be closed, or there could be an interruption in your home's gas supply.
- Dirty Flame Sensor: This safety device confirms a flame is present when the gas valve is open. If it's dirty, it can't detect the flame and will shut the furnace off.
- Faulty Limit Switch: This switch prevents overheating. If it malfunctions, it can shut the furnace down even when temperatures are normal.
- Clogged Condensate Drain: High-efficiency furnaces produce condensation. If the drain line is clogged, a safety switch will shut the system down to prevent water damage.
- Electrical Problems: Damaged wiring or a malfunctioning control board can also prevent your furnace from operating.
- Bad Blower Motor: If the blower motor fails, the furnace may ignite but won't be able to circulate warm air, causing it to overheat and shut down.
- Blocked Vents: Closed or blocked air vents can restrict airflow, leading to overheating and system failure.
What Should I Do If My Furnace Won't Turn On?
If you discover your furnace is not working, don't panic. Follow these simple troubleshooting steps to diagnose and potentially fix the problem before calling a professional.
- Check Your Thermostat: First, ensure the thermostat is set to "heat" and the temperature is set higher than the current room temperature. If it's battery-powered, replace the batteries.
- Inspect the Circuit Breaker: Go to your home's electrical panel and check if the furnace's breaker has tripped. If it has, flip it completely off and then back on to reset it.
- Check the Furnace Power Switch: Look for a power switch on or near the furnace unit itself and make sure it is in the "on" position.
- Confirm the Gas Supply Is On: If you have a gas furnace, ensure the gas valve near the unit is open. Also, check that other gas appliances in your home are working to confirm there isn't a supply outage.
- Examine the Pilot Light or Ignition System: For older furnaces, check if the pilot light is out. If it is, follow the manufacturer's instructions to relight it safely. For modern systems with electronic ignition, a failure may require professional furnace service.
- Replace the Air Filter: A clogged furnace filter is a very common culprit. Check your filter and replace it if it appears dirty to restore proper airflow.
- Clean the Flame Sensor: If the furnace turns on for a few seconds and then shuts off, a dirty flame sensor is a likely cause. You can often clean it carefully with a soft cloth.
- Ensure Vents Are Open: Walk through your home and make sure all air vents and registers are open and not blocked by furniture, rugs, or other items.
- Clear the Condensate Drain (For High-Efficiency Models): If you have a high-efficiency furnace, check the condensate drain line for any clogs and clear them to allow proper drainage.
- Look for Error Codes or Listen for Noises: Modern furnaces may display blinking error codes on a control panel. Note any codes or unusual sounds, as they can help a technician diagnose the problem faster.
- Call a Professional: If you've tried these steps and your furnace is still not turning on, it's time to call your local Bryant dealer. Complex issues with a control board, blower motor, or internal fuse require an expert.
When to Call a Bryant Dealer for Your Furnace Not Turning On
If furnace troubleshooting doesn't solve the issue, a trusted Bryant dealer can provide expert furnace repair or furnace replacement. Our technicians are highly trained to diagnose the root cause of the problem and deliver an effective, lasting solution. Regular furnace maintenance from a Bryant dealer can also prevent future breakdowns and ensure your system runs efficiently all winter.
Schedule an appointment with your local Bryant dealer today.
Furnace Not Turning On FAQs
To manually restart your furnace, turn off the power, wait a few minutes, then reset the thermostat and turn the system back on—check the breaker and filter as well.
Ensure the thermostat is set to heat and the temperature is above room level, replace the filter if dirty, and check for tripped breakers or a closed gas valve.
Common causes include a malfunctioning thermostat, tripped circuit breaker, clogged air filter, or a faulty ignition system preventing the furnace from starting.
Your furnace may not turn on due to power issues, a dirty flame sensor, low gas supply, or a safety switch that’s been triggered.
Dirty filters, tripped breakers, or thermostat issues are the most common causes.
Check the thermostat settings, power switch, and air filter before calling for service.
Turn off power to the furnace, wait a few minutes, then restore power and follow the manufacturer’s reset instructions. Consult your owner’s manual for details.
Learn More About Furnaces
- Learn how much is a new furnace
- Get help with a furnace leaking water
- Find out how long does a furnace last
- Find out how to fix a furnace blowing cold air
- Learn about the importance of furnace cleaning
- Understand the ins and outs of a furnace tune-up
- Read about furnace inspections
