Furnace Not Turning On the First Cold Day? What to Check, the Reset Button Question, and Which Burning Smells Are Normal
Quick answer
Furnace not turning on? Start with the thermostat batteries and mode, the power switch near the furnace, and the blower door, which has to be fully closed for the furnace to get power. Then check the filter and, on a high-efficiency furnace, the condensate drain. If those look right, read the blinking error light and call a technician for gas, ignition or safety switch problems.
Every October in Northern Virginia, the first chilly morning brings two kinds of calls. One is a furnace not turning on after six months of sitting idle. The other is a burning smell from the vents. Most of the time the cause is small.
Furnace not turning on? Start with these 5 checks
These checks need no tools and don’t involve gas. Give the furnace a few minutes after each one, since a normal start takes a minute or two.
1. The thermostat
You can fix this
A blank screen usually means dead batteries. Replace them even if the screen looks fine, since weak batteries can keep the display on and still fail to signal the furnace. Set the mode to HEAT. After a summer of air conditioning, it’s often still on COOL. Set the temperature 3 degrees above the room, and check that a hold or vacation setting isn’t overriding your schedule. For a smart thermostat that keeps dropping out, see our thermostat repair page.
2. The furnace power switch and the breaker
You can fix this
Most furnaces have a service switch that looks exactly like a light switch. It’s usually on the wall or a joist near the unit, or on the furnace itself. People flip it off by mistake, thinking it runs a light. Make sure it’s ON, then check the breaker. If the breaker trips again right away, leave it off and call.
3. The blower door
You can fix this
The lower front panel presses a small safety switch when it’s in place. If the door is crooked or loose, that switch cuts power to the whole furnace. This often happens right after a filter change. Lift the panel off and set it back firmly so it seats evenly.
Furnace not turning on after the easy checks?
We can usually be there the same day across Prince William and Fairfax counties. Use code FREECALL and the service call is free with your repair.
4. A clogged air filter
You can fix this
A badly clogged filter starves the furnace of air, so it overheats and trips its high-limit safety. After enough trips, many control boards lock the furnace out. Put in a clean filter with the arrow pointing toward the furnace, then reset power as described below.
5. A full condensate trap or pump
Maybe a DIY fix
High-efficiency furnaces, 90% AFUE and up with white PVC vent pipes, make water as they run. If the trap, drain line or condensate pump backs up, a float switch or the pressure switch keeps the furnace from starting. Look for standing water or a pump that hums but won’t empty. Water inside the furnace cabinet is a reason to call.
Thermostat clicks but the furnace doesn’t turn on
That click is the thermostat calling for heat, so the problem is at the furnace. The usual suspects are these:
- No power at the furnace, from the service switch, the breaker or a blown fuse on the control board
- An open safety, such as the door switch, high-limit switch, condensate float switch or rollout switch
- A control board in lockout after several failed starts, or a failed board
- A loose or broken thermostat wire
Gas, ignition and safety parts
Call a technician
When a furnace not turning on gets past every easy check, the fault is usually in the start-up sequence. The inducer motor starts, the pressure switch proves the vent is clear, the igniter heats, the gas valve opens and the flame sensor confirms flame. An inducer that hums with nothing after it points to the pressure switch, its tubing or the vent. An igniter that glows with no flame points to the gas supply or gas valve. Burners that light and drop out in seconds usually mean a dirty flame sensor. Our furnace repair technicians test each step to find the one that failed.
Read the blinking error code before you reset
The fastest clue for a furnace not turning on is the small LED on the control board. On most modern furnaces it blinks a fault code you can see through a sight glass in the blower door. Count the flashes and match them to the chart on the inside of the furnace door. Read it before you cut power or open the door, because on many furnaces that clears the code. A short phone video works well.
Is there a reset button on a furnace?
Most gas furnaces don’t have a true reset button. To reset the control board after a lockout, turn the service switch off, wait about 30 seconds and turn it back on. The furnace then tries to start again.
Some furnaces have a small manual-reset button on a rollout switch near the burners. It trips when flame rolls out of the burner area instead of going up the flue, often because of a blocked flue or a heat exchanger problem. Don’t keep resetting it. It tripped for a reason, and running the furnace again can be dangerous.
Older oil burners have a red reset button. Press it once at most, because repeated presses can flood the burner with oil. Oil heat is rare in Northern Virginia.
Burning smell on the first cold day: normal or not?
A dusty, slightly burnt smell the first time the heat runs is normal. Dust settles on the heat exchanger over the summer and burns off within 30 to 60 minutes. Open a window and let it run.
Shut the furnace off and call if you smell hot plastic or electrical burning, or if a burning smell lasts past the first hour or returns every time the heat runs.
A rotten-egg smell means gas. Don’t flip switches or restart the furnace. Leave the house and call your gas company or 911 from outside. If your carbon monoxide alarm sounds, get everyone out to fresh air and call 911. The U.S. Consumer Product Safety Commission recommends CO alarms on every level of the home and outside sleeping areas.
A furnace not turning on is a different problem from one that runs but won’t warm the house. For that, see our post on a furnace blowing cold air.
From our technician
“If I had to give you a rough split on no-heat and cold-air calls, flame-sensing problems are around 3 out of 10. Igniters are maybe 2 out of 10. Another 2 out of 10 are pressure-switch, inducer or venting problems. The rest are thermostat or power issues, limit switches, boards, gas valves and airflow.
I don’t like guessing from the symptom, though. On a gas furnace I watch the startup sequence and see where it stops. That usually tells you where to go next.”
Nick, Senior Technician, EPA-certified, experience since 2008
When to call a technician
- Your furnace is not turning on after the thermostat, switch, door and filter checks
- The breaker trips again when you reset it
- The rollout switch has tripped, or the furnace locks out again after a power reset
- The burners never light, or light and go out
- Water inside the cabinet, or a burning smell that won’t go away
Furnace repair in Northern Virginia
A furnace not turning on is a common call on the first cold days of October. Woodland handles furnace repair across Prince William, Fairfax, Loudoun and Fauquier counties, plus Arlington and Alexandria. We’re based in Woodbridge, so Woodbridge, Manassas, Dumfries and Lorton are usually same-day calls, and we’re in Fairfax, Centreville, Springfield, Arlington and Alexandria every week. See our furnace repair page or call (703) 335-1009.
What a visit costs with Woodland
You get a flat quote before any work starts, and our heating repair visits cover gas furnaces and heat pumps.
$69
Service call, waived completely when you go ahead with the repair
$99
Heating or AC tune-up to catch problems before the season turns
90 days
Warranty on parts and labor
Same price any day we’re open, including evenings and Saturdays. There’s no travel fee.
Frequently asked questions
Why is my furnace not turning on after summer?
The usual reasons are a thermostat still on COOL or with weak batteries, a service switch flipped off, or a blower door that isn’t seated. A clogged filter or full condensate pump can also stop it.
Is there a reset button on a furnace?
Most gas furnaces reset when you turn the service switch off for about 30 seconds and back on. A manual-reset rollout switch shouldn’t be reset repeatedly, because it trips for a safety reason. Oil burners have a reset button you should press only once.
Why does my thermostat click but my furnace doesn’t turn on?
The click means the thermostat is calling for heat, so the problem is at the furnace. Check the power switch, breaker and blower door. If those are fine, a safety switch, the control board or the wiring needs a technician.
Is a burning smell normal when I first turn on the heat?
A dusty smell for the first 30 to 60 minutes is normal. An electrical or plastic smell, or one that keeps coming back, is not. Turn the furnace off and call.
Can you fix a furnace not turning on the same day?
We can usually be there the same day in most of Prince William and Fairfax counties, so call early. The visit is a $69 diagnostic, waived with the repair, with a flat quote before any work.
Need a repair? We can usually be there today.
Locally owned and operated in Woodbridge. Licensed & insured, EPA 608 certified, with 15+ years fixing appliances, heating and cooling across Northern Virginia. $69 service call, free with the repair.
