Furnace Won't Turn On? Safe Checks Before You Call
Short answerWhen a furnace won't turn on, first check the thermostat setting and batteries, the breaker, the power switch, the furnace door and the filter. If it still won't run, call a heating technician. If you smell gas or a CO alarm sounds, leave and call from outside.
Safety first
- If you smell gas, leave right away and call 911 or the gas company from outside. Do not touch switches or the thermostat.
- If a carbon monoxide alarm sounds, go outside, call 911 and do not go back in until responders say it is safe. Headache, dizziness and nausea can be signs of CO.
- Do not remove burner panels, bypass safety switches or try to relight a furnace that keeps shutting off.
Likely causes
| Cause | How to tell | What fixes it |
|---|---|---|
| Thermostat setting or batteries | The screen is blank, or the system is not set to heat. | Set it to heat, set the temperature above the room temperature, and put in fresh batteries. |
| No power to the furnace | The breaker is tripped or the power switch on or near the furnace is off. | Reset the breaker once and turn the switch on. |
| Furnace door not closed | The blower panel is loose or was recently removed. | Seat the panel securely so the door safety switch closes. |
| Clogged filter or blocked vent | The furnace runs briefly, then shuts off. The filter is dirty, or the outdoor vent is covered with snow or debris. | Replace the filter and clear the outside vent. |
| Failed ignition, sensor or control | All of the above checks are fine, and the furnace tries to start and stops. | A technician tests and replaces the part. |
Why this is a job for a professional
- The checks did not bring the heat back, or the breaker trips again.
- You see rust or cracks on the flue or vent, notice burning smells, or the furnace shuts down repeatedly. Stop using it until a technician checks it.
- Ask: what failed? Did you check the heat exchanger, gas pressure and venting? Is it safe to keep running? Is repair or replacement a better value at this age?
What it costs to have fixed
Furnace Replacement is estimated at $2,950 to $8,350 nationally. See your state
Common questions
Why won't my furnace kick on?
Check that the thermostat is set to heat and above room temperature. Then check the batteries, the breaker, the furnace power switch and the door panel. If those are fine, it needs a technician.
Why is my furnace not igniting?
The cause may be the gas supply, burner or a safety control. Those involve gas and combustion, so leave them to a technician rather than trying to relight it repeatedly.
How often should a furnace be serviced?
CPSC advises having the heating system inspected and serviced every year, including the vents and chimney.
How do I reset my furnace?
Carrier says to turn off the furnace's power switch or the circuit breaker, wait 30 seconds, and turn it back on, and to call a dealer if a manual reset button trips again right away. We recommend leaving that button to a technician. If you smell gas or a carbon monoxide detector goes off, Carrier says to evacuate immediately and call emergency or utility services from a safe location. Source
Do furnaces have fuses?
Many do. A Rheem furnace manual shows a 3-amp fuse on the integrated control board and says the furnace's power must come through a circuit with the correct fuse or breaker. Fuse sizes vary by model, and a technician should check a furnace that keeps losing power. Source
Why is my furnace not turning on but getting power?
Carrier lists a dirty flame sensor, blocked air vents, a tripped limit switch and a faulty ignition among the causes, and says a fault can lock the furnace out. We recommend calling a technician once you have checked the thermostat and filter. If you smell gas, leave right away and call emergency or utility services from a safe location, as Carrier advises. Source
How do I know if my furnace is broken?
Carrier says to seek professional repair if you hear banging, grinding or squealing, or if basic checks do not bring it back. If you smell rotten eggs or the CO alarm goes off, evacuate right away and call emergency or utility services from a safe place. Source
Related repairs
- AC Freezing Up? Why It Happens and What to Do
- AC Not Cooling? What to Check Before You Call
- Smell Gas in Your House? Leave Now, Then Call
- Thermostat Not Working? Blank Screen and Other Fixes
Last verified 2026-11-01
Sources
- Resideo: T1 Pro Non-Programmable Thermostat User Guide — Checking the breaker, the system power switch, the furnace door, thermostat mode and setting, and batteries
- CPSC: Carbon Monoxide Fact Sheet — Symptoms, what to do when an alarm sounds, not using a faulty appliance until serviced, and annual heating system inspection
- CPSC: Check Home Heating System Before Winter Cold Sets In — What a qualified technician should check, including controls, safety devices and venting
- ENERGY STAR: Maintenance Checklist — Monthly filter checks and contractor checks of gas connections, burner combustion and heat exchanger
- U.S. Fire Administration: Carbon Monoxide Poisoning Prevention — Keeping furnace vents clear of snow and debris, and CO alarm placement
General information, not professional advice. Conditions, codes and prices vary. Turn off power, gas or water before any work, and hire a licensed professional when in doubt. Cost figures are our estimates, not quotes.