Furnace Not Blowing Hot Air? 7 Common Causes & Repair Costs (2025)

[Last Updated: October 15, 2025]

Waking up to a cold house on the first chilly morning of fall is a homeowner’s rite of passage. There are few things more uncomfortable than hearing your furnace kick on, only to feel cool or lukewarm air coming from the vents. The good news is that this common problem isn’t always a sign of a catastrophic failure. Often, it’s a simple issue you can fix yourself in minutes.

This guide will walk you through the 7 most common causes for a furnace not blowing hot air, starting with easy DIY checks. We’ll also provide estimated professional repair costs for the more complex problems, so you can know what to expect when you call for help.

Start Here: The Simple DIY Checks (Before You Call a Pro!)

Before you schedule an expensive service call, perform these four simple checks. These steps can solve the majority of common furnace issues and save you hundreds of dollars.

1. Check Your Thermostat Settings

This is the most common culprit. It sounds obvious, but a wrong setting is a frequent oversight. Make sure your thermostat is set to HEAT (not COOL or OFF), the fan is set to AUTO (not ON, which runs the fan continuously), and the temperature is set several degrees higher than the current room temperature to trigger the heating cycle.

Cost to Fix: $0

2. Check for a Clogged Furnace Filter

Just like with your AC, a dirty filter is the number one cause of furnace problems. A clogged filter restricts airflow, which can cause your furnace’s heat exchanger to overheat. As a safety measure, the furnace will shut down the burners to prevent damage, but the fan may continue to run, blowing cool air.

How to Fix: Locate the filter compartment on your furnace, slide out the old filter, and replace it with a new one of the same size. This should be done every 1-3 months during heating season.

Cost to Fix: $15 – $30 for a new filter.

3. Check the Pilot Light or Ignition System

If you have an older furnace (15+ years), it may have a standing pilot light that has gone out. Look for instructions on the furnace panel to safely relight it. Newer furnaces have electronic ignition systems. Try power-cycling your furnace: turn it off at the breaker, wait 30 seconds, and turn it back on. This can sometimes reset a faulty ignition sequence.

Cost to Fix: $0

4. Check the Circuit Breaker

Your furnace is on its own circuit. Go to your home’s breaker panel and find the one labeled “Furnace” or “HVAC.” If it’s tripped to the middle or OFF position, flip it completely OFF and then back ON once to reset it.

Cost to Fix: $0

When to Call a Pro: Common Mechanical & Electrical Failures

If the DIY checks didn’t solve the problem, the issue likely involves a faulty component that requires professional diagnosis and repair. For your safety, do not attempt to repair these issues yourself.

5. Faulty Thermocouple or Flame Sensor

This is a safety device that senses a flame. If it’s faulty or dirty, it will shut off the gas supply to the burners to prevent a gas leak, even if the ignitor is working. The burners might light for a few seconds and then go out.

Estimated Cost: $150 – $350. This is a common and relatively inexpensive professional repair.

6. Malfunctioning Blower Motor

The blower motor is the powerful fan that pushes the heated air through your home’s ducts. If the motor or its capacitor fails, the furnace might produce heat, but it has no way to circulate it. You’ll hear the furnace ignite but feel no air coming from the vents.

Estimated Cost: $150 – $450 to replace a capacitor, or $500 – $1,500+ to replace the entire motor.

7. Failed Ignitor or Bad Control Board

If your furnace clicks as if it’s trying to start, but the burners never light, you could have a failed electronic ignitor. If the furnace behaves erratically or doesn’t respond at all, the “brain” of the system—the control board—may have failed.

Estimated Cost: $200 – $400 for an ignitor replacement; $500 – $1,200 for a new control board.

Summary of Potential Repair Costs

Final Word: Prioritize Safety

While fixing the issue yourself is satisfying, a furnace combines natural gas, open flames, and high-voltage electricity. When in doubt, always call a professional. The safety of your home and family is paramount. If the simple DIY checks don’t restore your heat, don’t wait for the first deep freeze—schedule a service call with a qualified HVAC technician.

Ethan Cole

I’m a dedicated content creator and researcher with a strong passion for technology, innovation, and digital culture. At Howh.net, I focus on delivering well-researched, accurate, and engaging articles that help readers understand complex topics in a simple and practical way. My goal is to inform, inspire, and make reliable information