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A furnace not turning on is usually caused by a thermostat set wrong, dead thermostat batteries, a tripped breaker, a switch turned off, a clogged filter or a closed gas valve. If those check out, a failed ignitor or dirty flame sensor is likely. Try the quick checks below first. If heat still will not start, call for heating services in Belmont.
The first cold snap in Gaston County brings a wave of these calls, because furnaces sit unused all summer. Gerald Griffin Heating and Cooling Services has restored heat to local homes since 2013. If you smell gas, leave the house first and call your gas company. For no heat, call us at (980) 277-5122, 24 hours a day.
Key Takeaways
- Check the thermostat, breaker and furnace switch before anything else.
- A loose blower door or clogged condensate line can stop a furnace from starting.
- Press a reset button only once. Repeated trips point to a safety problem.
- Many NC homes use heat pumps, which have different causes than gas furnaces.
- Never ignore a gas smell or a carbon monoxide alarm.
Why Is My Furnace Not Turning On?
Most furnaces that will not turn on have a simple problem: the thermostat is not calling for heat, the furnace has no power or a safety switch has stopped it. Less often, a part like the ignitor, flame sensor or control board has failed. The checks below cover the easy causes in about 15 minutes.
Is It a Gas Furnace or a Heat Pump?
This matters in North Carolina. The EIA reports that 62% of homes in North Carolina heat mainly with electricity, while about 29% use natural gas.
Gas Furnaces
A gas furnace has a burner, an ignitor and a flame sensor. You may see a gas line and a white or metal vent pipe. Most of this guide applies to gas furnaces.
Heat Pumps and Electric Air Handlers
If you have a heat pump, the indoor unit is an air handler with electric heat strips. It often has its own breaker, separate from the outdoor unit. If the air handler breaker trips, you get no heat at all. For heat pump trouble, see our heat pump repair service.
10 Quick Checks Before You Call for Repair
- Thermostat mode, setpoint and batteries
- Furnace power switch
- Circuit breaker
- Blown fuse
- Blower door closed tight
- Air filter
- Gas valve
- Pilot light on older furnaces
- Condensate line and float switch
- Outside intake and exhaust pipes
1. Check the Thermostat
Set it to Heat and raise the temperature 5 degrees above the room. Replace the batteries if the screen is blank or dim. After a summer of cooling, many thermostats are still set to Cool.
2. Check the Furnace Power Switch
Look for a light switch on or near the furnace. It is easy to flip off by mistake. Make sure it is on.
3. Check the Circuit Breaker
Find the breaker labeled furnace or air handler. If it is tripped, switch it fully off, then on. If it trips again, stop and call a pro.
4. Check for a Blown Fuse
Some furnaces have a fuse box near the unit. A blown fuse has a broken wire or a dark window. Replacing a fuse inside the furnace control board is a job for a technician.
5. Close the Blower Door Tight
Most furnaces have a safety switch that stops the unit when the front panel is loose. If you recently changed the filter, press the panel firmly back in place.
6. Replace a Dirty Air Filter
A clogged filter can make the furnace overheat and shut down. ENERGY STAR recommends you check your filter monthly and warns that a dirty filter can damage equipment. Airflow problems alone can cut efficiency by up to 15%.
7. Check the Gas Valve
The gas valve handle should run parallel with the pipe. If it is crossways, it is closed. Also check that other gas appliances work. If none do, call your gas company.
8. Check the Pilot Light
Older furnaces have a standing pilot light. If it is out, follow the relighting steps on the label inside the furnace. If it will not stay lit, the thermocouple may need replacement.
9. Check the Condensate Line
High efficiency furnaces drain water through a small tube. If it clogs, a float switch stops the furnace. Look for water in the pan or a full condensate pump.
10. Clear the Outside Pipes
White PVC intake and exhaust pipes on the side of the house can get blocked by leaves, pine straw or nests. Clear anything you can reach safely.
Symptom Guide: What Your Furnace Is Telling You
| Symptom | Likely Cause | DIY or Pro? |
|---|---|---|
| Nothing happens at all | Thermostat, switch, breaker or fuse | DIY checks first |
| Fan runs but no heat | Gas valve, ignitor or flame sensor | Check valve, then call a pro |
| Clicking but no flame | Failed ignitor or gas supply problem | Pro |
| Lights, then shuts off in seconds | Dirty flame sensor | Pro |
| Blinking light on the furnace | Error code from the control board | Count flashes, then call a pro |
| Breaker trips again | Electrical short or motor problem | Pro |
Is There a Reset Button on a Furnace?
Many furnaces have one. It may be a red button on the blower motor or a rollout switch near the burners. Press it once. If the furnace shuts off again, do not keep pressing. A tripped reset button is a warning that something, like overheating or poor venting, needs a technician.
Blinking Lights and Error Codes
Many modern furnaces have a small status light you can see through a window in the lower panel. Count the flashes, then check the code chart on the furnace door or in the manual. Share that code when you call. It helps us bring the right part.
Problems That Need a Technician
- Failed hot surface ignitor that no longer glows
- Dirty or worn flame sensor
- Tripped limit or rollout switch
- Bad blower motor or capacitor
- Failed control board or gas valve
If your furnace starts but keeps shutting off, read our guide to furnace short cycling problems. For no heat at all, call Gerald Griffin at (980) 277-5122.
Safety First: Gas Smells, Carbon Monoxide and Space Heaters
If you smell rotten eggs, leave the house and call your gas company from outside. The EPA lists leaking or back-drafting furnaces as sources of carbon monoxide. Headaches, dizziness or flu-like symptoms that clear up when you leave home are warning signs. Keep CO alarms on every level.
Be careful with space heaters while you wait for repair. The U.S. Fire Administration reports that heating fires ranked second among causes of home fires in 2021, with an estimated 32,200 fires. Keep heaters 3 feet from anything that can burn and never leave them running unattended.
How to Keep Your Furnace From Failing Next Winter
- Schedule a heating tune-up every fall, before the first cold night.
- Check the filter monthly during heating season.
- Test your thermostat in October, not on the first freezing night.
- Keep outside vent pipes clear of leaves and pine straw.
The EPA also recommends a yearly professional inspection of furnaces and flues. Our heating maintenance plan options make that easy.
Furnace Not Turning On FAQs
How do I force my furnace to start?
You should not force a furnace to start. Set the thermostat to Heat, check the switch, breaker, blower door and filter, then press the reset button once if there is one. If it still will not run, a safety device is doing its job, and a technician should find out why.
Why is my furnace not responding to the thermostat?
A furnace that ignores the thermostat usually has dead thermostat batteries, the wrong mode selected, a loose wire or a tripped breaker. Smart thermostats can also lose power after an outage. Replace the batteries and check the settings. If it still does not respond, the wiring or control board needs testing.
What would cause a furnace to have no power?
No power usually comes from a furnace switch turned off, a tripped breaker, a blown fuse or a loose blower door safety switch. A failed control board or transformer can also cause it. Check the switch, breaker and door first. If the breaker trips again, call a technician.
How do you know if a furnace fuse is blown?
A blown cartridge fuse near the furnace may look burnt or have a broken wire inside. A glass fuse may look dark or cloudy. If the furnace has no lights or sounds and the switch and breaker are on, a fuse may be blown. Control board fuses should be tested by a pro.
Get Your Heat Back On in Belmont and Gaston County
If you still have a furnace not turning on after these checks, call Gerald Griffin Heating and Cooling Services at (980) 277-5122. Our 24 hour emergency HVAC team serves Belmont, Mount Holly, Gastonia, Cramerton and nearby towns. We will find the cause, fix it safely and get your home warm again.
Gerald Griffin Heating and Cooling Services
902 Belmont Mt Holly Rd, Belmont, NC 28012
Phone: (980) 277-5122
Hours: Open 24 hours
NC Heating Contractor License #32307