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 and 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 and switch on the thermostat, you will usually find an option for the fan. This is generally a good starting point if your furnace fan not turning off as it is easy to overlook. Yet, many people find that this is 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 why you cannot 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 regulates the fan based on the current thermostat settings, temperature, and other factors. 

The system will consider various elements and then determine if the fan should be running. 

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 ensures the fan does not move too fast, but it could be the reason for a constantly running fan with incorrect settings. 

The fan limit switch can generally be automatic or a manual override mode. The system will use the built-in technology to determine the current situation’s best fan speed 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 must manually adjust the fan speed. If you fail to make adjustments, the fan may continue running without 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. You may have to scroll through some menus to reach this function if you have a digital thermometer. There might also be a dedicated button for the function. 

Consult the manual or a guide if you are unsure how to find the fan limit switch on your thermostat. Once you access 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 your manual settings. 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 and other parts of your HVAC solution. Several settings on the thermostat’s control panel regulate the furnace fan. Thus, when the furnace blower won 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 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. To diagnose the problem yourself, you must open up your thermostat’s control panel. The entire cover needs to be removed.

Once the cover is off, you should look closely 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.
• Ensure wires do not touch more than a single point on circuit boards.

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

Faulty Fan Switch

As mentioned, 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

If you wish to continue controlling the furnace fan, a replacement for the faulty switch will be needed. The process for replacing this switch depends on the model you have. You must carefully 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 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 for months… and the worst don’t even fix your oven. (But they charge you for it anyway.)

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FAQs

What should I do if my furnace fan won’t turn off?

If your furnace fan doesn’t turn off, there are a few things you can do:

• Check the thermostat settings. Make sure the thermostat is set to AUTO instead of ON. If it’s set to ON, the fan will continue running until you manually turn it off.
• Check the fan limit switch. The fan limit switch is a safety device that prevents the fan from running too long. If the fan limit switch is faulty, it may not turn off the fan.
• Check the wiring. There may be a problem with the wiring that is causing the fan to stay on.
• Call a professional. If you’re uncomfortable troubleshooting the problem, call a qualified HVAC technician.

What are the causes of a furnace fan not turning off?

There are a few possible causes of a furnace fan not turning off. Here are some of them:

• Faulty thermostat: If the thermostat is set to ON instead of AUTO, the fan will continue to run.
• Faulty fan limit switch: The fan limit switch is a safety device that prevents the fan from running too long. If the fan limit switch is faulty, it may not turn off the fan.
• Short circuit: If there is a short circuit in the wiring, it may keep the fan running.
• Bad relay: A bad relay may prevent the fan from turning off.
• Clogged filter: A clogged filter can restrict airflow, which can cause the fan to work harder and stay on longer.
• Overheating: If the furnace is overheating, the fan may stay on to help cool it down.
• Damaged motor: A damaged motor may be unable to turn off properly.

How do I fix a furnace fan that won’t turn off?

Steps on how to fix a furnace fan that won’t turn off:

1. Check the thermostat settings. Make sure the thermostat is set to AUTO instead of ON. If it’s set to ON, the fan will continue running until you manually turn it off.
2. Check the fan limit switch. The fan limit switch is a safety device that prevents the fan from running too long. If the fan limit switch is faulty, it may not turn off the fan.
3. Check the wiring. There may be a problem with the wiring that is causing the fan to stay on.
4. Replace the furnace filter. A clogged filter can restrict airflow, which can cause the fan to work harder and stay on longer.
5. Call a qualified HVAC technician. If you’re uncomfortable troubleshooting the problem, call a qualified HVAC technician.

hvac fan won t turn off

Your HVAC fan doesn’t turn off? there are a few possible causes. The most common cause is a faulty thermostat. If the thermostat is set to ON instead of AUTO, the fan will continue running until you manually turn it off.

Other possible causes include a faulty fan limit switch, a short circuit, a bad relay, a clogged filter, overheating, or a damaged motor. If you’re unsure what’s causing the problem, it’s best to call a qualified HVAC technician.

Here are some tips to prevent your HVAC fan from not turning off:

• Change your furnace filter regularly. A clogged filter can restrict airflow, which can cause the fan to work harder and stay on longer.
• Have your HVAC system serviced regularly. A qualified HVAC technician can inspect your HVAC system and ensure it runs properly.
• Be aware of the signs of a problem. If you notice that your HVAC fan is running more than usual or is not turning off, it’s important to have it checked by a qualified HVAC technician.

Steve Rajeckas

Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he’s not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.