Furnace Blower Not Working, or the Fan Won't Stop Running

Short answer: If the furnace blower won't come on, check that the thermostat is set to Heat with a setting above room temperature, that the filter isn't clogged, that the furnace door is fully closed, and that the breaker hasn't tripped. If the fan runs and never stops, the thermostat fan setting is usually on On instead of Auto. If those checks don't fix it, the cause is usually a blower motor, capacitor, control board or limit switch, which is a job for a technician.

Safety first: if you smell gas (a rotten-egg smell), leave the house now and call 911 or Southwest Gas from outside. If a carbon monoxide alarm sounds, get everyone out and call 911 from outside. A dusty or oily smell the first time the heat runs each season is normal and can linger for a couple of days.

Two different problems with the same part

The blower is the fan inside your furnace cabinet that pushes warm air through the ducts and out the vents. People search for "furnace blower not working" for two opposite reasons:

1. The blower won't come on. The furnace may click, the burners may even light, but no air comes out of the vents, or air comes out only for a moment.
2. The blower won't turn off. Air keeps moving through the house even when the heat isn't running, sometimes cool air.

They have different causes, so start by deciding which one you have.

When the blower won't come on: checks you can do

These are safe for any homeowner. Do them once, in order, and stop if one fixes it.

1. Thermostat settings

Set the system to Heat, the fan to Auto, and the temperature a few degrees above the current room temperature. If the screen is blank or dim, replace the batteries. Our thermostat guide covers blank screens, problems after a battery swap and after a power outage.

2. The filter

A filter packed with dust restricts airflow. That can make the furnace overheat, shut its burners off on a safety switch, and cycle the blower in short bursts. Las Vegas dust loads filters faster than many people expect. If you can't see light through it, replace it. Not sure of the size? See how to find your air filter size.

3. The furnace door

Most furnaces have a small safety switch behind the blower compartment door. If the door is loose or not seated, the furnace won't run the blower at all. Push the panel firmly into place.

4. Breaker and service switch

Look for a light-switch-style service switch on or near the furnace, often in a closet, garage or attic. Make sure it's on. Then check the breaker panel for a tripped furnace breaker. If you reset it once and it trips again, leave it off and call. A breaker that keeps tripping points to an electrical fault.

When the blower runs and won't stop

This one is often simpler.

• Fan set to On. On most thermostats, "On" runs the blower continuously, whether or not the furnace is heating. "Auto" runs it only during a heating or cooling cycle. Switch it to Auto and give it a few minutes.
• The thermostat's own schedule or circulate mode. Some smart thermostats have a circulate or fan-schedule feature that runs the fan for part of every hour. Check the fan menu.
• The furnace thinks it's too hot. If the heat exchanger overheats, the furnace keeps the blower running to cool it down. That often goes back to a clogged filter or closed vents. Our furnace limit switch guide explains this safety switch.
• A stuck relay or control board. If the fan runs even with the thermostat set to Off and the fan on Auto, the control board relay that switches the blower may be stuck closed. That needs a technician.

If the fan won't stop no matter what you set, you can turn the furnace's service switch off to stop it until a technician can look. You'll have no heat while it's off, so dress warm and close off unused rooms.

What usually causes a blower failure

When the simple checks don't solve it, these are the parts a technician usually tests:

• Blower motor. Motors wear out. Signs include a hum with no spin, a burning electrical smell from the cabinet (not the normal first-run dust smell), or a motor that's hot to the touch and stopped.
• Run capacitor. Many blower motors use a capacitor to start and run. A weak capacitor can leave the motor humming or spinning slowly.
• Control board. The board tells the blower when to start and stop. A failed relay or a fault code can stop the blower or keep it running.
• Limit or rollout switches. These shut parts of the furnace down when something overheats. They're doing their job; the real question is why it overheated.
• Wiring. Loose or rubbed wires at the motor or board.

If the blower motor squeals, grinds or rattles before it quits, our furnace noises guide can help narrow it down.

Why this matters in a Las Vegas winter

Las Vegas winters are mild by most standards, but nights do get cold. NOAA's 1991–2020 normals for Las Vegas put the average January low at 40.5°F and the average January high at 58.5°F. Many homes go months with the furnace barely used, then call on it hard the first cold week. A blower motor or capacitor that was fine last spring can fail on that first heavy run, and filters that sat all summer through AC season are often already loaded with dust.

What not to do

• Don't run the furnace with the blower door off or with the door switch taped down.
• Don't keep resetting a breaker that trips again.
• Don't try to spin a hot or stuck blower wheel by hand while the power is on.
• Don't take the motor or control board apart. Both carry line voltage.

When to call

Call a technician if the blower still won't run after the checks above, if it runs nonstop with the thermostat set to Off, if a breaker keeps tripping, or if you notice a hot-electrical or plastic smell from the cabinet. If warm air turned cold but the fan still runs, see heater blowing cold air instead. For a visit, see our Las Vegas furnace repair service.

FAQ

Why does my furnace click but the blower doesn't come on?

The furnace may be starting its sequence and then stopping on a safety switch, often from a clogged filter or overheating, or the blower motor, capacitor or control board may have failed. Check the thermostat, filter, door and breaker first. If it still won't run, call a technician.

Why does my furnace fan keep running when the heat is off?

The most common reason is the thermostat fan setting is on On instead of Auto. If it keeps running with the fan on Auto and the system set to Off, the control board relay may be stuck, which needs a technician.

Is it bad to leave the furnace fan on On all the time?

It isn't dangerous, but it runs the blower motor many more hours and moves unheated air between cycles, which can feel drafty. Most homes are comfortable with the fan on Auto.

Can a dirty filter stop the blower?

A badly clogged filter can make the furnace overheat and shut down on its limit switch, so the blower may run in short bursts or the furnace may stop heating. Replacing the filter is the first thing to try.

Can I replace a furnace blower motor myself?

We don't recommend it. The motor and its capacitor and control board carry line voltage, and the wrong motor or wiring can damage the furnace. A technician can test the motor, capacitor and board to find which part actually failed.

What hours can I reach Colton?

Colton Air Conditioning is open Monday to Friday, 8am to 5pm. You can call or book online during those hours.

Colton Air Conditioning

Colton Air Conditioning, 6545 S. Fort Apache Rd Ste 135 #467, Las Vegas, NV 89148. Nevada contractor license 0092120. Hours: Monday to Friday, 8am to 5pm. Call (702) 738-6976 or book online during those hours.

Want routine maintenance on a schedule? See our Comfort Club maintenance plans: Gold, Platinum and Diamond tiers are all listed there.