Problem guide
Furnace blower not working
The blower moves air for heating and for cooling. When it stops, both stop.
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Written by HYRE HVAC Research Desk Primary-source research, data analysis and fact checking
The short answer
A furnace blower not working is usually a thermostat fan setting, a door safety switch that is open, a tripped breaker, a failed blower capacitor, a burned-out motor or a control board fault. You can check the settings, door, filter and power.
If the blower hums without spinning or stays silent, switch the system off and call a technician, because running the burners without airflow overheats the furnace.
Check these first (safe DIY)
Set the thermostat fan to "on". If the blower starts, the motor works and the problem is in heating or cooling control. If it does not start, the fault is in the blower circuit.
Make sure the blower compartment door is fully seated. The furnace will not run with it open.
Check the service switch and breaker. Reset the breaker once.
Pull the filter. If you cannot see light through it, replace it. A clogged filter starves the system of airflow. ENERGY STAR suggests checking it monthly in heavy-use seasons.
What the symptoms point to
| What you notice | Likely cause |
|---|---|
| Blower hums but does not spin | Failed run capacitor, or a seized motor |
| Blower runs only on high, or only on "on" | Control board relay or wiring |
| Blower silent; burners light then shut off | Blower not starting; limit switch trips |
| Blower starts, then stops | Overheating motor, failing ECM module |
| Squealing or grinding | Worn bearings, loose blower wheel, belt on older units |
| Blower runs constantly | Fan set to "on", or a stuck relay |
Two kinds of blower motor
Older and basic furnaces use a permanent split capacitor (PSC) motor with a separate run capacitor. A failed capacitor is a common, modest repair.
Many newer furnaces use an electronically commutated motor (ECM), with a control module on the motor. ECM failures can be in the module or the motor itself, and parts are often specific to the furnace model. Knowing which you have helps you follow the quote.
ENERGY STAR’s maintenance checklist includes cleaning and adjusting blower components, because a dirty blower wheel cuts airflow, and airflow problems can reduce efficiency by up to 15 percent.
When to stop and call
Do not open the outdoor unit, furnace cabinet or control box. Capacitors can hold a dangerous charge with the power off, and line-voltage work is for a licensed technician.
Switch off the furnace and call.
Leave the house, then call the gas utility or 911 from outside. Do not touch switches, the thermostat or your phone indoors.
Leave the house and call 911 from outside.
What a technician will check
Expect tests of the control board output to the blower, the capacitor, motor windings or the ECM module and its signals, the door switch and the limit switch.
They will check the blower wheel for dirt and balance. The written diagnosis should say what failed and why. On an older furnace with a motor failure, see repair vs replace.
What drives the repair price is the motor type, the part and labor. HyreHVAC publishes no prices yet; use the repair cost calculator with your own quote.
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Questions
Why is my furnace fan not turning on?
Can I replace a furnace blower capacitor myself?
Why does my furnace blower hum but not spin?
Why is my furnace blower running constantly?
Does the blower affect my AC?
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HYRE HVAC Research Desk
Primary-source research, data analysis and fact checking
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