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Furnace Fan Won’t Turn Off? Top 4 Causes (+ Easy Fixes)

Repairing a broken furnace can cost as much as $1,000 on average, with a cost dependent on the issue at hand. There are many cases where serious problems started small, yet the homeowner failed to address the issue when insignificant. When the furnace fan doesn’t turn off, it is important to take appropriate action. 

If your furnace fan won’t turn off, your thermostat may need to be switched to AUTO, the limit switch may be in manual mode, and there may be faulty wiring or switches. You should make sure a manual override has not been programmed, and take a look at the limit switch that controls the fan. 

In this article, I’ll discuss common reasons for a furnace fan not turning off, as well as explain the fixes that can be used in each of these situations. I’ll also share the easiest way to fix this problem. (Check the bottom of the article.)

Let’s get started!

Thermostat Isn’t on “AUTO” Position

When you inspect the settings switch on the thermostat, you will usually find an option for the fan. This is generally a good starting point, as it is an easy one to overlook. Yet, many people find that this ends up as the reason why the furnace fan won’t turn off. 

The thermostat fan switch will usually have three different settings. This includes ON, OFF, and AUTO. Many people turn the switch to the “ON” function. This means the thermostat is going to continue running at all times. It could be the reason why you cannot seem to get the fan to switch off. 

How To Fix

If the problem lies with the fan setting on your thermostat, this will usually be a quick fix. 

Start by finding the location of this switch. Take a look at the current setting. If the fan is set to the “ON” setting, you want to switch it to “AUTO” instead. The AUTO setting allows for the fan to be regulated based on the current thermostat settings, temperature, and other factors. 

The system will take various elements into account and then determine if the fan should be running or not. 

Here’s a video to give you a better idea of the difference between ON and AUTO settings:

Fan Limit in Manual Override Mode

The fan’s current state can be controlled through settings on the thermostat, but other functions can also be adjusted through the control panel. One of these includes the fan limit switch. This switch serves to ensure the fan does not move too fast in general, but it could be the reason for a constantly running fan with incorrect settings. 

The fan limit switch can generally be set to automatic or a manual override mode. The system will use the built-in technology to determine the current situation’s best fan speed with automatic. This is done after the system takes the temperature into account and compares this to the settings you configured. 

With manual override mode, you will need to adjust the fan speed manually. If you fail to make adjustments, the fan may continue to run without any limitations. 

How To Fix

This is another one that can be an easy fix in many cases. You will first need to understand how to reach the fan limit switch. If you have a digital thermometer, you may have to scroll through some menus to reach this function. There might also be a dedicated button for the function. 

Consult the manual or a guide if you are not sure how to find the fan limit switch on your thermostat. Once you gain access to the switch, take a closer look at the current setting. 

  • If the fan is set to manual override on purpose, you may have to make a few adjustments to the manual settings you use. This could include implementing additional limits for the fan function, for example. 
  • It may be a more effective option to set the fan limit switch to automatic. This way, you won’t have to worry about constantly changing the setting as the weather changes. The system will instead deal with these needed changes on its own. 

The specific settings depend on the system you have installed. Here is a video that gives you a quick video demonstration of how a manual fan limit switch works:

Faulty Wiring in the Thermostat

A thermostat is an electric device that is connected to your furnace. It is used to regulate several functions in the furnace, as well as other parts of your HVAC solution. Several settings on the thermostat’s control panel handle the regulation of the furnace fan. Thus, when the furnace fan doesn’t turn off, it is important to consider faults with its thermostat. 

Multiple wires can be found inside the thermostat control panel. Each of these wires is connected to circuit boards that control the furnace setup’s various elements. When any one of these wires is faulty, it could cause problems – including a fan that does not shut off when it is supposed to. 

How To Fix

This is a more complicated fix that may be best left to the professionals. If you want to diagnose the problem yourself, you will need to open up your thermostat’s control panel. The entire cover needs to be removed.

Once the cover is off, you should take a closer look at all the wires inside. 

  • See if you can find any wires that have come loose.
  • Check for burn marks on the circuit boards and the wires.
  • See if there are wires that have been bent too much.
  • Make sure wires are not touching more than a single point on circuit boards.

If you find one of the problems listed above, fixing this could help bring back control over the furnace fan. 

Faulty Fan Switch

As we mentioned previously, a manual override on the fan limit switch can cause problems. There are, however, cases where you may find that the switch itself is faulty. When this is the case, adjusting the fan limit settings will not affect the device – as the communication between the switch and the fan is disrupted. 

How To Fix

A replacement for the faulty switch will be needed if you wish to continue having control over the furnace fan. The process for replacing this switch depends on the model you have. You will need to be careful to ensure all connections are placed according to the instructions provided. 

However, this is generally a task that a professional should do, which reduces the chances of making mistakes and causing further damage to the system. Here’s a video explaining how the switch can be replaced or repaired:

Since the thermostat is connected to an electrical system, it is best not to touch wires or anything if you are not experienced. I recommend contacting an HVAC expert to help diagnose the problem and fix the source’s furnace fan issue.

The Easiest Fix for a Furnace Fan That Won’t Turn Off

If you don’t have the time or expertise to troubleshoot and fix your furnace, the smart decision — as you know — is to hire a furnace repair expert to fix it for you.

The problem is that finding a trustworthy and affordable repair service — and actually booking an appointment with them — can feel like pulling teeth.

Some services never call you back. Others charge criminally high rates. The best options are often booked out for months… and the worst don’t even fix your oven. (But they charge you for it anyway.)

To save you from that teeth-grinding frustration and bring you fast and affordable repairs from top-rated pros, I’ve partnered with a helpful company called Networx.

They work with thousands of contractors across the United States, and they make it easy for you to get free furnace repair quotes from the best repair services near you.

Here’s how it works in 7 easy steps:

  1. Go to the form below.
  2. Select your type of furnace in the dropdown menu. Options include Electric Furnace, Gas Furnace, Oil Furnace, and Propane Furnace.
  3. Add some basic contact information and a brief description of your problem. (Your information will only be used to provide you with furnace repair quotes.)
  4. Click the “Get Free Quotes” button when you’re done.
  5. Our repair service partner will contact multiple vetted furnace repair experts near you. They’ll explain your problem and ask each service to contact you with a free quote.
  6. You’ll receive an email or phone call with repair quotes from each service. You can choose the most affordable option and schedule your repair directly with them.
  7. They’ll come to your house and fix your oven. Problem solved!

Using this form to find the best repair rates is 100% risk-free. There is zero obligation to hire any of the vetted contractors who contact you.

Fill out the form now to get free quotes from trusted furnace repair services in your area.