If your furnace is not turning on, the most common cause is either a dirty air filter, a tripped circuit breaker, or a thermostat set incorrectly. Most homeowners fix this in under 30 minutes at zero cost. If those three checks do not solve it, you are likely looking at a repair bill of $150 to $600 for an ignitor, limit switch, or blower issue. Only about 5 to 10 percent of non-starting furnaces need full replacement, which runs $2,800 to $7,500 installed.
This guide walks you through all seven causes in order from easiest to hardest, so you can fix it yourself if possible and know exactly what a technician will say when you call.
Safety First: Check for Carbon Monoxide
Before you start poking around your furnace, make sure your carbon monoxide detector is working. A cracked heat exchanger, one of the causes we cover below, can leak CO without any visible sign. If your CO alarm is going off or you feel dizzy or nauseous, leave the house immediately and call 911.
The U.S. Consumer Product Safety Commission recommends a CO detector on every floor of your home and one within 10 feet of each sleeping area.
7 Reasons Your Furnace Won’t Turn On
1. Thermostat Is Set Wrong or Has Dead Batteries
This sounds obvious, but it is the number one call HVAC technicians get. Check these in order:
- Mode: Make sure it is set to HEAT, not COOL or FAN ONLY.
- Temperature: The set temperature must be higher than the current room temperature by at least 3 degrees to trigger the furnace.
- Batteries: Most programmable thermostats use AA or AAA batteries. Weak batteries cause erratic behavior or complete shutdown.
- Schedule: A programmed schedule may have the heat turned off during certain hours.
Cost to fix: $0 to $10 for new batteries.
If you have a smart thermostat like a Nest or Ecobee, check the app to see if the schedule or away mode is blocking heating. Also verify the thermostat is still connected to your Wi-Fi.
2. Clogged or Dirty Air Filter
A dirty air filter is the single most common cause of furnace shutdowns in the US. When airflow is blocked, the furnace overheats and the safety limit switch cuts power to protect the heat exchanger.
Here is how to check it:
- Find your filter, usually in the return air duct near the furnace or in a wall/ceiling vent.
- Hold it up to a light source. If you cannot see light through it, replace it.
- Standard 1-inch filters should be replaced every 30 to 90 days depending on pets, dust, and occupancy.
Cost to fix: $5 to $30 for a replacement filter. Do not reuse disposable filters.
If your filter was very dirty, the limit switch may need 30 to 45 minutes to reset after you replace the filter and restore airflow. Turn the thermostat off, change the filter, wait 30 minutes, then try again.
3. Tripped Circuit Breaker or Blown Fuse
Furnaces draw a lot of power on startup. A power surge, a failing motor, or even a momentary grid fluctuation can trip the breaker.
Go to your electrical panel and look for:
- A breaker labeled FURNACE or HVAC in the tripped position (usually in the middle between ON and OFF).
- If you have an older fuse box, look for a blown fuse.
To reset: Flip the breaker fully to OFF, then back to ON. If it trips again immediately or within a few minutes, do not keep resetting it. A repeatedly tripping breaker means something is drawing too much current, which could indicate a failing blower motor or a short circuit. Call a technician.
Also check the furnace itself. Most furnaces have a separate power switch that looks like a standard light switch, usually on the wall near the unit or on the furnace cabinet. It is easy to accidentally switch it off.
Cost to fix: $0 to reset a breaker. $150 to $400 if the breaker itself is faulty and needs replacement by an electrician.
4. Pilot Light Is Out or Electronic Ignitor Has Failed
If you have an older furnace (pre-2000), it likely has a standing pilot light. If you have a newer unit, it uses an electronic ignitor (hot surface ignitor or spark ignitor).
Standing pilot light: Look through the small window on the furnace cabinet. You should see a small blue flame. If it is out, follow the relighting instructions printed on the furnace door. These typically involve turning the gas valve to PILOT, holding down the reset button, and using a lighter or match to relight the flame. The American Gas Association recommends consulting the manual or a technician if the pilot light will not stay lit, as this can indicate a faulty thermocouple.
Electronic ignitor: These glow orange like a toaster element just before the burners ignite. A failed hot surface ignitor is one of the most common furnace repairs. Signs include hearing the furnace click on, the inducer fan running, but no heat or flame.
Cost to fix: Hot surface ignitor replacement costs $150 to $300 for parts and labor. A thermocouple on an older furnace runs $75 to $150.
5. Clogged Condensate Drain Line (High-Efficiency Furnaces)
If your furnace is high-efficiency (90 percent AFUE or above), it produces condensation during operation. This water drains out through a PVC condensate line. If that line clogs with algae or debris, the furnace shuts down via a float switch to prevent water damage.
Signs of a condensate issue:
- Water pooling around the base of the furnace.
- Error code on the control board indicating a condensate fault (check your manual or look up the blinking light sequence for your model).
- Gurgling sounds near the drain.
To fix it yourself: Find the condensate drain line (a white or gray PVC pipe running to a floor drain or utility sink). Use a wet-dry shop vac to suck out the clog from the drain end. You can also flush it with a mixture of one cup water and one tablespoon of white vinegar.
Cost to fix: $0 to $20 DIY. $75 to $200 for a technician.
6. Faulty Blower Motor or Capacitor
The blower motor pushes heated air through your ductwork and into your living spaces. If the motor or its start capacitor fails, you may hear the furnace attempt to start, the burners ignite briefly, and then the system shut off because no air is moving.
Signs of blower motor problems:
- You hear the burners fire but feel no air from the vents.
- A humming or buzzing noise from the furnace cabinet.
- The furnace runs for a few minutes then shuts off.
A bad capacitor (the component that gives the motor a startup boost) is a cheaper fix than replacing the motor itself.
| Component | Average Repair Cost |
|---|---|
| Start/run capacitor | $150 to $300 |
| Blower motor (single speed) | $300 to $500 |
| Blower motor (variable speed) | $500 to $850 |
| Control board | $400 to $700 |
This repair requires a licensed HVAC technician. Capacitors store electrical charge and can be dangerous to handle without proper training.
7. Cracked Heat Exchanger
This is the most serious issue on this list, and fortunately the rarest. The heat exchanger is the metal component that separates the combustion gases from the air you breathe. A crack in the heat exchanger allows carbon monoxide to leak into your home.
Signs of a cracked heat exchanger:
- CO detector alarm.
- Yellow or flickering burner flames instead of steady blue.
- Soot or black marks around the furnace.
- Unusual odor near the unit.
If a technician diagnoses a cracked heat exchanger, they are required by law in most states to shut down the furnace until it is repaired or replaced. Heat exchanger replacement costs $1,500 to $4,000 in parts and labor alone. On a furnace that is 15 or more years old, replacement of the entire unit is almost always the better financial decision.
Cost to fix: Heat exchanger replacement: $1,500 to $4,000. Full furnace replacement: $2,800 to $7,500 installed (varies by unit type, efficiency rating, and region).
Quick Diagnostic Checklist Before Calling a Tech
Run through these in order before scheduling a service call. You can save $100 to $200 in diagnostic fees:
- Thermostat is set to HEAT and temperature is set above current room temp
- Thermostat batteries replaced within the last 12 months
- Air filter checked and replaced if dirty
- Furnace power switch is in the ON position
- Circuit breaker for the furnace is not tripped
- Condensate drain is clear (high-efficiency furnace only)
- Furnace door is fully closed and latched (safety interlock switch)
- Gas shutoff valve near the furnace is in the open position (parallel to the pipe)
How Much Does Furnace Repair Cost by Problem?
| Problem | DIY Fix | Pro Repair Cost |
|---|---|---|
| Thermostat calibration/batteries | $0 to $10 | $75 to $100 diagnostic |
| Dirty air filter | $5 to $30 | $75 to $100 |
| Tripped breaker | $0 | $100 to $200 |
| Ignitor replacement | Not recommended | $150 to $300 |
| Thermocouple replacement | $20 to $40 (advanced DIY) | $75 to $150 |
| Condensate drain clearing | $0 to $20 | $75 to $200 |
| Capacitor replacement | Not recommended | $150 to $300 |
| Blower motor replacement | Not recommended | $300 to $850 |
| Control board replacement | Not recommended | $400 to $700 |
| Heat exchanger replacement | Not recommended | $1,500 to $4,000 |
| Full furnace replacement | Not recommended | $2,800 to $7,500 |
Diagnostic fees range from $75 to $125 in most US cities. Many HVAC companies waive the diagnostic fee if you proceed with the repair.
When to Repair vs. Replace Your Furnace
A helpful industry rule: if the repair cost exceeds 50 percent of the value of the furnace, and the furnace is more than 10 to 15 years old, replacement is usually the smarter choice. The Department of Energy recommends replacing any furnace with an AFUE rating below 80 percent with a modern high-efficiency unit (95 percent or above), which can reduce heating costs by 15 to 40 percent.
Look for the ENERGY STAR label when shopping for a replacement. Furnaces that earn ENERGY STAR certification meet strict efficiency guidelines set by the EPA and may qualify for federal tax credits.
Federal tax credit: Under the Inflation Reduction Act, homeowners who install an eligible high-efficiency furnace (90 percent AFUE or above) may qualify for a 30 percent tax credit, up to $600 per year. See IRS Form 5695 for details.
State-by-State Cost Differences
HVAC labor rates vary significantly across the US:
| Region | Average Diagnostic Fee | Average Repair Cost (Ignitor) |
|---|---|---|
| Northeast (NY, MA, CT) | $100 to $150 | $250 to $400 |
| Midwest (IL, OH, MI) | $75 to $115 | $175 to $300 |
| Southeast (FL, GA, NC) | $75 to $100 | $150 to $250 |
| Southwest (TX, AZ, NM) | $75 to $110 | $160 to $275 |
| West Coast (CA, OR, WA) | $100 to $150 | $200 to $350 |
Rates also rise significantly from November through February due to high demand. If your furnace is aging, schedule a tune-up in September or October before technician calendars fill up.
What to Ask When Calling an HVAC Company
When you call for a service visit, ask these questions upfront:
- What is the diagnostic fee, and is it waived if I proceed with the repair?
- Is the technician licensed in my state?
- Do you offer a warranty on parts and labor?
- Are you available for emergency same-day service, and what is the additional charge?
You can verify HVAC contractor licensing through your state’s contractor licensing board. The National Association of Home Builders maintains a directory of licensed contractors by state.