If your furnace won't turn on, the cause is usually something simple: a thermostat that's off, set to Cool, or out of batteries; a tripped breaker or furnace power switch; a clogged filter; or an open furnace door panel. Check those first. If they're all fine, the problem is likely a failed igniter, a dirty flame sensor, a gas supply issue, a clogged condensate line, or a bad control board, and those need a licensed technician. The Air Company of GA offers furnace repair, open 24 hours across Atlanta and nearby cities. Call 404-583-7788 any time.
Quick Checks Before You Call (5 Minutes or Less)
Most "dead furnace" calls on the first cold mornings in Atlanta, Sandy Springs and Marietta turn out to be one of these. They're safe for any homeowner to check.
- Thermostat settings. Make sure it's set to Heat (not Cool or Off) and the set temperature is at least 3 degrees above the room temperature. If the screen is blank, replace the batteries. Our guide to a blank thermostat screen walks through the other causes.
- Furnace power switch. Most furnaces have a light-switch-style switch on or near the unit, often in the basement, attic or a closet. It's easy to flip off by mistake when you're storing things.
- Circuit breaker. Look for a tripped breaker labeled furnace, air handler or HVAC. Reset it once. If it trips again, leave it off and call us, since that points to an electrical fault.
- Air filter. A filter packed with dust can cause the furnace to overheat and shut itself off on a safety limit. Swap it, and make sure the airflow arrow points the right way.
- Door panel. Furnaces have a safety switch that keeps them from running if the front panel isn't seated all the way. Press it closed firmly.
- Gas supply. If you have gas heat, check that the gas valve at the furnace is open (the handle runs parallel to the pipe) and that other gas appliances are working.
Smell gas? Don't touch switches or try to restart anything. Leave the house and call your gas provider or 911 from outside. Our post on preventing carbon monoxide leaks covers other safety warning signs.
Common Reasons a Furnace Won't Turn On
1. Failed Hot Surface Igniter
Most modern gas furnaces light the burners with a hot surface igniter instead of a standing pilot. Igniters are fragile and wear out over time. When one cracks, you'll often hear the inducer fan start, then nothing lights, and the furnace tries again a few times before locking out. Older furnaces with a standing pilot have their own issues, covered in why a furnace pilot light keeps going out.
2. Dirty Flame Sensor
If the burners light for a few seconds and then shut off, a dirty flame sensor is a common culprit. The sensor confirms there's a flame; when it's coated with buildup, the furnace thinks the flame failed and shuts the gas off for safety. Cleaning it is a routine part of a tune-up.
3. Clogged Condensate Line or Pressure Switch Problem
High-efficiency furnaces produce water that drains through a small line. If that line or its trap clogs, a safety switch can keep the furnace from firing. A blocked vent pipe or a weak inducer motor can also stop the pressure switch from closing, which prevents ignition.
4. Tripped Limit Switch From Overheating
Restricted airflow from a dirty filter, closed vents or a failing blower motor can make the furnace overheat. The limit switch shuts it down to protect the heat exchanger. If this keeps happening, it can lead to the furnace turning on and off all day, or not starting at all.
5. Bad Control Board or Blown Fuse
The control board runs the whole startup sequence. A power surge or a short can blow the small fuse on the board or damage the board itself. Many boards flash a blinking light code that tells a technician exactly what failed.
6. Wiring or Thermostat Communication Issues
Loose thermostat wires, a damaged low-voltage line in the attic or a failing thermostat can keep the "call for heat" from ever reaching the furnace. If you're thinking about an upgrade, see our thermostat installation page.
7. Heat Pump Systems: Different Causes
If your home uses a heat pump instead of a gas furnace, a no-heat problem can come from a frozen outdoor coil, a failed defrost control, low refrigerant or a bad backup heat strip. Learn more on our heat pump service page and in emergency heat vs. aux heat.
When to Repair and When to Replace
Most of the problems above are affordable, same-visit repairs. Replacement starts to make sense when the furnace is near the end of its life, needs a major part like a heat exchanger, or breaks down every winter. Our signs you may need a new furnace post covers what to look for, and our furnace installation team can give you an honest comparison. As a Bryant dealer, we install high-efficiency gas furnaces and heat pumps sized for your home.
Prevent No-Heat Calls With a Fall Tune-Up
Many furnace failures show up on the first cold night because small problems go unnoticed all summer. A yearly tune-up cleans the flame sensor, checks the igniter, clears the condensate line and tests safety controls before you need heat. Our maintenance plan is $159 per year for your first system and $60 for each additional unit, and members get priority scheduling. It's one of the best values in the city.
Furnace Repair Near You, Open 24 Hours
The Air Company of GA is a family-owned HVAC company with NATE-certified technicians, serving homes and businesses in Atlanta (including Buckhead, Midtown and Virginia Highland), Sandy Springs, Marietta, East Cobb, Smyrna, Vinings, Roswell, Alpharetta, Johns Creek, Duluth, Norcross, Peachtree Corners, Brookhaven, Dunwoody, Chamblee, Doraville, Tucker and Decatur. We're open 24 hours, so if your furnace won't turn on tonight, call 404-583-7788 or visit our furnace repair page. See our full service area.
Frequently Asked Questions
Why won't my furnace turn on even though the thermostat is set to heat?
If the thermostat is on Heat and set above room temperature, check the furnace power switch, the circuit breaker, the air filter and the front door panel. If those are fine, the cause is often a failed igniter, a dirty flame sensor, a clogged condensate line or a control board problem, which a technician should diagnose.
Why does my furnace start and then shut off after a few seconds?
A furnace that lights and then shuts off within seconds usually has a dirty flame sensor. The sensor can't detect the flame, so the furnace shuts off the gas as a safety measure. Overheating from a clogged filter can also cause short shutdowns.
Is it safe to reset my furnace myself?
You can safely reset a tripped breaker once, turn the furnace power switch off and on, and replace the filter. If the breaker trips again, the furnace repeatedly locks out, or you smell gas, stop and call a professional.
How much does it cost to fix a furnace that won't turn on?
The cost depends on the cause. Many no-heat problems, such as a dirty flame sensor, a bad igniter or a clogged drain, are relatively affordable repairs. We'll diagnose the problem and give you a clear price before any work starts.
Do you offer emergency furnace repair at night or on weekends?
Yes. The Air Company of GA is open 24 hours for furnace and heating repair across Atlanta, Sandy Springs, Marietta, Roswell, Alpharetta, Decatur and nearby cities. Call 404-583-7788 any time.
How can I keep my furnace from breaking down this winter?
Change your filter regularly and schedule a yearly heating tune-up before cold weather. Our maintenance plan is $159 per year for the first system and $60 for each additional unit, with priority scheduling for members.
