Why does my furnace blower start then shut off?

Author: Randal Carroll  |  Last update: Tuesday, February 25, 2025

Check Your Flame Sensor If this becomes dirty or corroded, it can cause short cycling and result in your furnace blower shutting off and on frequently. You can clean the flame sensor yourself with a rag or brush and some rubbing alcohol, but if it doesn't work, you may need to call a professional for help.

Why does my furnace blower turn on then shut off?

This can be caused by a couple of possibilities. It's not that you're blower is out of sync, it is either going bad or if this is an older furnace with a fan-limit switch, it is cooling down the heat exchanger too fast (or the unit is underfired) and the fan switch is turning it off.

Why does my furnace blower start then stop then start again?

This can be caused by a couple of possibilities. It's not that you're blower is out of sync, it is either going bad or if this is an older furnace with a fan-limit switch, it is cooling down the heat exchanger too fast (or the unit is underfired) and the fan switch is turning it off.

Why does my furnace kick on and then kick off?

The top causes to blame when a furnace kicks on and off are: The air filter needs changed. The thermostat batteries need to be replaced. Blower motor malfunctions.

Why won't my furnace blower motor stay on?

Check the circuit breaker, thermostat settings, and air filter first as these are common causes of furnace fan failure. Inspect electrical connections, listen for unusual noises, and verify proper airflow through vents during operation.

Furnace Starts Then Stops - Troubleshooting | Repair and Replace

Why does my blower motor shut off after a few seconds?

Inspect the Fan Limit Switch for Damage or Shorts

Limit switches control how often your furnace blower turns on and off. If these become damaged or shorted out due to age or wear, this can cause them to malfunction and lead to cycling issues.

How do you reset the blower on a furnace?

Learning how to reset your furnace blower motor is relatively simple, but there are a few steps to follow:
  1. Step 1: Turn Off the Power. ...
  2. Step 2: Inspect the Blower Motor. ...
  3. Step 1: Locate the Furnace Blower Motor Reset Button. ...
  4. Step 2: Press and Hold the Reset Button. ...
  5. Step 3: Check the Circuit Breaker.

Why does my furnace kick on but not stay on?

Insufficient airflow or insufficient gas pressure. A defective, malfunctioning ignition board, flame sensor, light switch, thermostat, thermocouple, fan limiter, or draft inducer fan. The drainage line is blocked, resulting in a full condensate pan. Temperatures are so low that the furnace cannot stay lit.

Why does my blower motor keep going out?

It most commonly occurs when the blower fan motor becomes aged or is overworked. A lack of regular maintenance is generally to blame for blower fan burnout.

Why does my furnace turn on for a second then shut off?

There are multiple reasons why your furnace is short cycling. These could include a dirty filter, blocked vent, or malfunctioning flame sensor. You can switch for a clean furnace filter, or have your HVAC technician resolve a more complicated issue.

Why does my furnace try to start then stop?

Restricted airflow

Blocked vents or a clogged air filter may cause your furnace to run and then shut off too early. It's easy to fix these issues on your own. You should change your furnace filter at least once every three months. Follow our guide to do it yourself.

How do you know if you have a bad flame sensor?

Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies. This is a frustrating problem, but an HVAC technician can fix it.

Why does my furnace blower motor only work sometimes?

Problems include dirty filters, broken wires, poor voltage supply and faulty limit switch or capacitor. You can test your limit switch with a multimeter, and clean the blower motor's wire coils. If this doesn't work, you may need to replace your furnace blower motor.

How do you know if blower motor is bad in furnace?

If you suddenly hear loud and strange sounds like squealing or grinding, these are symptoms of a bad furnace motor blower that can signal signs of motor bearing problems or a damaged belt in older belt-driven models. Repairs may be possible or it may be time to replace the blower motor entirely.

What would cause a furnace blower not to kick on?

Check for Electrical Issues: Inspect the furnace circuit for blown fuses and reset circuit breakers if necessary. Inspect the Air Filter: Examine the air filter for debris and dust buildup and replace it if dirty. Clear Obstructions: Ensure there are no obstructions near the blower wheel that might hinder its rotation.

How do I know if my thermostat is bad?

7 Ways to Tell Your Thermostat Is Broken
  1. The Thermostat Has No Power. ...
  2. The AC or Furnace Won't Turn On. ...
  3. The Heater or AC Won't Turn Off. ...
  4. The Thermostat Reading Doesn't Match the Room Temperature. ...
  5. The Thermostat Doesn't Respond. ...
  6. The HVAC System Is Short Cycling. ...
  7. The Thermostat Forgets Programmed Settings.

Why does my furnace blower keep turning on and off?

Your furnace blower fan may repeatedly cycle due to a clogged air filter, a malfunctioning thermostat, inadequate airflow, or issues with the furnace's limit switch. Each of these issues can disrupt the blower's operation.

How do I know if my blower control module is bad?

  1. Symptoms of a Bad Blower Motor Control Module.
  2. A blower motor control module is crucial for your vehicle's HVAC system. ...
  3. * No Airflow or Weak Airflow.
  4. One of the most telling signs is if the blower motor isn't blowing air at all or the airflow is weaker than usual. ...
  5. * Intermittent Operation.

What does a damaged thermocouple look like?

Failed Thermocouple Symptoms

The first is signs of contamination on the tube, which can include discoloration, cracks, or pinholes. Next, check the wiring for any signs of wear or corrosion like missing insulation or bare wire.

Where is the reset button on my furnace?

In most newer systems, the button is often directly next to the blower motor, while in older systems, it may be harder to spot as it is sometimes underneath or behind the motor. The reset button is often made of yellow or red plastic and marked with a large “R ” to make it easier to spot.

How do you know if your furnace needs to be reset?

Why Your Furnace May Need To Be Reset
  1. The furnace has overheated: When your furnace runs too hot, it triggers a safety shut-off to prevent damage. ...
  2. The fuel supply is empty: Your furnace can't generate heat without fuel. ...
  3. The gas valve is shut: A closed valve blocks the fuel supply.

What turns the blower motor on a furnace?

The blower motor contains a capacitor, a device that stores energy to help the motor turn over with a jolt of extra electricity when it first starts up. If the capacitor goes bad, electricity may not reach the motor or it may not have enough electric to power the motor for its initial spin.

Where is the blower motor reset button on a carrier furnace?

Carrier furnaces typically have a small reset button inside the burner compartment. It may be red or yellow and is usually labeled “Reset.” If you're unsure where to find it, consult your furnace's user manual. Hold the button down for about 10 seconds before releasing it.

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