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Why Does My Furnace Blower Run Constantly?

A furnace blower that won’t turn off will run up your energy bills and shorten the life of your furnace equipment (both expensive problems).

So if your furnace blower won’t turn off and you want to fix it, check first for:

  • A thermostat that’s set incorrectly
  • A fan limit switch that’s in its “continuous on” mode

We’ll show you exactly what to look for when troubleshooting your thermostat and fan limit switch and explain when you’ll need a professional to fix your furnace.

Already know you need a professional? Just contact us and we’ll send out a tech right away.

First, check your thermostat settings

Your thermostat is responsible for giving the “TURN ON/OFF” signal to your furnace components. So if your blower fan just won’t stop running, the first place to check is at the thermostat.

Two settings that you’ll want to check are:

1) The fan setting

Your thermostat fan setting should be set to AUTO, not ON. You see, ON forces the blower to run 24/7 whereas the AUTO setting only runs the blower when your furnace is on a heating cycle.
 

Keeping your thermostat fan setting to ON will also cause cold air to blow out of your air vents. The only time we suggest using the ON setting for your fan instead of AUTO is when you’re cleaning and dusting.

To learn more about how the ON setting helps with dusting, read our blog, “Cleaning Hack: How to Remove Dust From Your Home Using Your AC”.

2) The set temperature

It’s also possible that you’ve set your thermostat’s set temperature too high, forcing your furnace to heat constantly as it struggles to keep your home at such a high temperature. To make sure you haven’t asked too much of your furnace, try lowering your thermostat 5 degrees lower than the current room temperature.

If you’ve tried both of the above and your furnace blower is still blowing non-stop, then move on to checking your fan limit switch.

Next, check your fan limit switch

Your fan limit switch is the control that turns your furnace blower on and off. This switch is located just under the furnace hood

If that fan switch is set to MAN (manual) or ON, it will force the blower to run continuously. Follow the steps below to check the settings of your fan limit switch:

  1. Remove the panel from your furnace and locate your fan limit switch.
  2. Check the small white button on the switch. If the white button is pressed in, your fan limit switch is set to manual and is forcing your blower to run constantly.
  3.  
  4. If the button is currently pressed in, just depress the white button to reset it to AUTO mode (blower mode only runs during heating cycles).

Furnace blower still running non-stop? Contact a Minnesota tech

If you’ve tried all of the troubleshooting steps above, you may have problems with your thermostat wiring or have a bad fan limit switch.

Either way, you’ll need a professional to fix those problems. Just contact us and we’ll send over a professional right away.

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Categories: Heating