Is your furnace refusing to start? Before you call for emergency service, check the basics. The most common reasons a furnace won’t turn on are:
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Incorrect Thermostat Settings
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Dirty/Clogged Air Filters
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Tripped Circuit Breakers
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Closed Gas Valves
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Tripped Safety Sensors
Below, Thiele Heating & Air Conditioning breaks down how to check each of these issues safely and when it’s time to call a professional.
Reasons Why Your Heater Won’t Turn On
No two furnace problems are exactly the same. A heater may fail to turn on because of one specific issue or a mix of conditions that trigger a shutdown. Below are five of the most common reasons a furnace won’t turn on and what they typically mean.
1) Thermostat or Temperature Setting Issues
Thermostat settings are one of the first things to check when heat won’t turn on. The system needs to be set to heating mode, and the desired temperature must be higher than the current room temperature. Dead batteries or a malfunctioning thermostat can also prevent the furnace from starting. In some cases, the furnace is fine, but the thermostat simply isn’t sending the signal to produce heat.
2) Dirty Air Filters and Restricted Airflow
Dirty air filters and clogged furnace filters are a very common cause of furnace problems. When proper airflow is blocked, the system has to work harder and may shut itself down for safety. Restricted airflow can trigger a safety switch and stop the furnace from producing warm air altogether. Replacing dirty filters regularly helps the system operate properly and prevents unnecessary shutdowns.
3) Power Supply or Electrical Issues
A furnace needs a steady power supply to run. Tripped circuit breakers, blown fuses, or issues inside the electrical panel can cut power to the system. Many furnaces also have a power switch that looks like a light switch and can be turned off accidentally. Faulty wiring, loose wiring, or fuse blows can also prevent the furnace from running or cause it to shut off repeatedly.
4) Gas Supply or Ignition Problems
Gas furnaces rely on a steady gas supply and a working ignition system. A closed gas valve, issues with the gas line, or an interrupted fuel supply will prevent the furnace from igniting. Older furnaces may experience pilot light problems, while newer systems may have a failing furnace ignitor or ignition system. Without ignition, the furnace can’t begin producing heat.
5) Safety Sensors or Internal Component Problems
Modern HVAC systems are designed to shut down when something isn’t safe. A dirty flame sensor, dirty burners, a clogged condensate drain, or a tripped safety switch can all cause the furnace to stop running. Internal issues like a failing blower motor, control board problems, error codes, or damage to the heat exchanger also fall into this category. These issues typically require a trained HVAC technician to diagnose and repair safely.
If you ever smell gas, stop immediately. Do not try to restore power or restart the furnace. Leave the home, contact your gas company, and then schedule an emergency furnace repair with a professional once it’s safe.
Quick Troubleshooting for When Your Furnace Won’t Turn On
Some furnace issues are simple enough to spot without tools or technical knowledge. Others aren’t safe—or possible—to fix on your own. Before scheduling service, it can be worth trying a few basic checks to rule out the obvious. If anything feels unsafe or unclear, stop and contact an HVAC professional right away.
- Confirm the thermostat is calling for heat. Make sure the thermostat is set to heating mode and the temperature is set several degrees above the current room temperature. Replace thermostat batteries if the screen looks dim or unresponsive.
- Check for lost power to the furnace. Look at the electrical panel for tripped breakers or a blown fuse. Restore power once if needed, but don’t keep resetting breakers. Also check the furnace power switch near the unit—it may look like a standard light switch.
- Replace the furnace filter if it’s dirty. Pull out the furnace filter and inspect it. If it’s packed with dust, replace it before trying to restart the system. Dirty filters can cause airflow problems that prevent the furnace from running.
- Make sure gas and vents are not blocked. Confirm the gas valve near the furnace is open. Check that supply vents and return vents around the home aren’t blocked by furniture, rugs, or closed registers.
If the furnace won’t turn on after these steps, or nothing happens at all when the system tries to start, the issue is likely inside the furnace itself. At that point, further furnace troubleshooting isn’t helpful and can risk damaging the system. That’s when you need the local furnace repair company near you to come out and take over.
Heat Won’t Turn On? Here’s How Thiele Can Help
If the heat won’t turn on, you want answers—and you want them fast. Thiele Heating & Air Conditioning has been fixing furnaces across Central Indiana since 1883. As a trusted Indianapolis furnace repair company, we’ve seen just about every reason a furnace can stop working.
Our HVAC technicians work in communities like Noblesville, Carmel, Pendleton, Lawrence, Plainfield, Mooresville, Greenfield, Beech Grove, Greenwood, Whiteland, and Franklin. That means help is nearby when your furnace won’t turn on.
Here’s what to expect during your furnace repair:
- Inspection and Diagnosis: We inspect the furnace and find what’s keeping it from turning on. That includes checking the thermostat, power supply, gas valve, ignition system, sensors, and airflow.
- Plan and Pricing: Once we know what’s going on, we explain it clearly and go over your options. You’ll know what can be repaired and what it will cost before any work starts.
- Expert Furnace Repairs: Once the issue is identified, we handle the repair and get the furnace running again. That may include replacing a faulty ignitor, cleaning a dirty flame sensor or burners, fixing wiring or control issues, clearing a condensate drain, or addressing a gas supply problem.
Many furnaces that won’t turn on can be repaired. If a furnace replacement is required or makes more sense financially, we’ll be upfront about that. If it can be fixed and should be fixed without costing you more, that’s what we’ll recommend.
Schedule Your Furnace Repair with Thiele Heating & Air Conditioning
Furnace breakdowns bring a lot of questions and concerns—cost, timing, and who you’re letting into your home. At Thiele Heating & Air Conditioning, we’re fast, we’re fair, and we’re focused fully on you. You have enough stress right now, and we don’t add to it. With over a century of experience behind us, you can trust that the Thiele name means you’ll be taken care of. Call us at (317) 561-5273 or message us today for your furnace repair in the greater Indianapolis area.