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It's not uncommon for a Honeywell thermostat fan won't turn off but an HVAC fan that won't turn off and runs on its own for hours can be indicative of a problem. 

In addition to the annoying sound, if a fan is running continuously, it will add to your energy bill and also reduce the lifetime of your equipment. So it’s best to check why your fan is continuously running and then solve the issue.

In this article, I walk through 8 troubleshooting steps, starting with the most common reason: incorrect fan settings on your thermostat.

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if, in any doubt, it is best to seek the assistance of a professional.

How your HVAC Fan or Blower Should Work

Under normal conditions, the fan only turns on when the thermostat signals a need for increased airflow to maintain your desired temperature.

This means that the fan will work in tandem with your HVAC system, circulating the hot or cold air (depending on your temperature setting) and switching off when the desired temperature is reached.

However, if your best Honeywell thermostat fan refuses to turn off, there could be a problem with the communication between the thermostat and the fan, or a hardware malfunction within the fan itself.

In both cases, this can lead to wasted energy and increased wear on your system. Therefore, it’s necessary to adjust the fan settings or troubleshoot for any hardware faults.

Why a Continuously Running Fan or Blower is Not a Good Sign

It might not feel like such a big issue at first but a fan or blower that’s running indefinitely can cause many problems down the line.

  • For starters, a thermostat fan running continuously can create energy wastage and lead to skyrocketing energy bills. 
  • Beyond that, it can shorten the lifespan of your air filters and also cause the indoor temperature to fluctuate.
  • For example, a fan that won't turn off during the winter may lead to your indoor temperature being slightly cooler than you'd prefer. 
  • Meanwhile, during summer, too much air circulation in your home can turn the indoor temperature to get uncomfortably warm – which will put undue strain on your AC. 

Also, let's not forget that a stubborn fan can be a sign of more significant concerns. As such, it requires immediate attention to keep it from snowballing into something more expensive to fix. 

Fan

Reasons Why Your Honeywell Thermostat Fan Won’t Turn Off

There are several reasons why your HVAC fan or blower won’t turn off. In most cases, it’s because of the thermostat settings but can also be due to an underlying hardware fault. 

So let’s go through these, one by one.

1. Thermostat Settings

Typically, the fan mode setting on Honeywell thermostats will have two (or three) settings: On, Auto, and Circ (for circulating). 

The On setting will help switch the fan to run continuously. When you choose this function, the fan will run indefinitely regardless of whether the cooling or heating systems are on or off. 

Fan “Auto” Setting

  • The Auto setting enables the thermostat to control the fan only when it activates the heating or cooling systems.
  • Essentially, this means the fan won't operate unless it's accompanied by either the heater or the air conditioner.
  • Choosing the Auto setting is what I recommend since it promotes energy efficiency and lowers utility costs.
  • The Circ setting, on the other hand, makes the fan run intermittently, approximately 20 minutes per hour.
  • This option is typically used during times when indoor temperatures are naturally comfortable, such as spring or fall, and don't require additional heating or cooling.
  • If your fan won't turn off, it's likely that your thermostat is set to “On” rather than “Auto.”

To remedy this, you can adjust the setting accordingly. Check the guides below or refer to my collated list of Honeywell manuals to browse a specific model.

App and Model-Specific Guides to Changing Fan Settings

Honeywell App

If the Honeywell thermostat fan won't turn off, try changing the fan settings through the app: 

  1. Open the Honeywell Home app on your smartphone or other smart device.
  2. Then, find and select your thermostat from the list of connected devices.
  3. Tap on the “Fan” option located at the bottom of the thermostat screen.
  4. Adjust the setting to your desired preference (Auto, On, or Circulate).
  5. To save the changes, tap on “Save” or “Done” and your thermostat fan should switch to the correct setting.
Honeywell Home App Fan Settings 1
Changing fan settings via the Honeywell Home app

If you haven't set up your Honeywell thermostat with the supported apps, I highly suggest doing so. Not only will you be able to control the thermostat remotely, but you'll also be able to integrate it into Google Home, Alexa and other smart home hubs.

You can download the apps below.

T9 and T10 Models

Smart Thermostat with a color touchscreen

T10 Pro 3

For the T9 and T10 Pro models follow these steps: 

  1. If the menu icon (three horizontal lines) isn't visible on the home screen, tap the screen to wake the display.
  2. Then, touch the menu icon at the bottom of the screen.
  3. Tap on the “Fan” option.
  4. After that, choose the setting you want for the fan to run (Auto, On, or Circulate)
T10 Pro Fan Settings
How to change the fan settings on a Honeywell T10 Pro smart thermostat

Please keep in mind that the fan option might not be available for all system types.

T6/T5/T4/6000 and 5000 Series

Smart and programmable thermostats

T4 T5 T6 and 6000 series

For these models, you can change the fan settings by tapping on the “Fan” option on your thermostat's home screen to cycle between available fan modes. 

After the display shows the setting you want (between Auto, On, and Circ) you can leave the screen as is.

T6 Pro Smart Fan Settings
Switching fan modes in a Honeywell T6 style smart thermostat

9000/8000 Series

Smart thermostats with touchscreen

90008000 series all 1 1

For these models with a large touchscreen display, you can change the fan settings by:

  1. Tap on “FAN” to access fan settings.
  2. Choose from On, Automatic, Circulate, or Follow Schedule.
  3. Press Done to save and exit.
9000 series fan settings
Changing fan settings on a Honeywell 9000 series thermostat

For these models, the “Follow Schedule” fan option sets the fan or blower to run according to your programmed schedule. To override this, you can tap on “Auto” or “On.”

4000/3000/2000/1000 Models

Programmable and non-programmable thermostats

40002000 models 1 1

To control the fan settings on these older models:

  1. Locate the Fan Switch on your thermostat, you should find a toggle switch labeled “Fan” on one of the sides or corners of the device.
  2. Then, identify the fan switch positions. Usually, it’s an option between “Auto” and “On.”
  3. Gently flip the switch between “Auto” and “On” according to your needs.
4000 series fan switch
Changing fan settings on older Honeywell thermostat models

2. Extreme Temperatures

Another common cause why your Honeywell thermostat fan won't turn off is extreme weather events. 

For instance, if the temperature takes a drastic drop or rises uncontrollably – it can force your HVAC system to keep the fan working overtime to maintain your preferred indoor temperature. 

Size and Capabilities of Your HVAC System

This problem generally occurs when the HVAC system is too small to handle climate control for the given space (or the drastic change in temperatures).

Besides that, it might be struggling because it wasn’t serviced or maintained for some time. 

Whatever the case, your HVAC system will keep the fan on as a means of sustaining the temperature, at least until the weather improves.

3. Faulty Sensors

Bad sensors can also be why your HVAC / Honeywell thermostat fan won't turn off. If your temperature sensor is faulty, your thermostat is running blind. 

If a sensor cannot gauge the temperature of a room correctly, it's sending inaccurate results to the thermostat. This can prompt the thermostat to keep the fan switched on, especially since you don’t have a dedicated setting to turn it off.

The easiest way to check for a faulty sensor is to use a digital thermometer for the most accurate reading. If the room temperature in the thermostat display and the thermometer don't match up – you've found the root of the problem. 

Temperature and Humidity Sensors

4. Honeywell Thermostat Fan Won't Turn Off: Faulty Thermostat

Because of software glitches or hardware faults within the thermostat itself, it can cause the fan to run indefinitely, even when you’ve turned the setting to “Auto”. 

So to figure out if the thermostat itself is faulty, you can try removing it from the wall mount and check for fan operation. Here’s how:

  1. Using the model-specific guides above, change the thermostat fan setting to “On.”
  2. Then, take out the panel from the wall mount. You might have to unscrew it first.
  3. If you notice the fan or blower starting to power down as soon as you remove the thermostat, it will confirm that the issue is with the thermostat itself.
  4. Otherwise, if the fan keeps on blowing air, you can safely rule out the thermostat.

If the thermostat is faulty, you might have to get it replaced. You can do this yourself but I recommend contacting an HVAC professional to see if they can repair it first.

5. Thermostat Wiring

Most modern thermostats have a separate wire for controlling the fan. It's green in color and is attached to the G terminal at the back of your thermostat. However, most new thermostats also require an additional C-wire, which many household systems do not have. 

So technicians often refurbish the fan wire as the C-wire and do not connect any wire to the G terminal. In this case, the fan remains on indefinitely, since it is not being controlled exclusively by the thermostat.

You can easily ascertain if this is the case by first checking to see if your thermostat needs a C-wire to run. If yes, then remove the thermostat's cover to reveal the backplate. If there's no wire attached to the G terminal, you may need to change the wiring to settle the fan issue.

Besides that, the wires may be damaged or exposed, so check for these as well or get the help of an HVAC technician.

Honeywell T10 Wiring
Wiring connections on a Honeywell thermostat wall mount

6. Stuck/Damaged Relay

The relay switch acts as the intermediary between the thermostat and HVAC equipment, bridging the gap between their differing voltage requirements.

It enables them to work in sync, despite the thermostat being low DC voltage and the HVAC running on mains power.

When the relay malfunctions, the connection between the thermostat and HVAC equipment is disrupted, potentially causing issues like a constantly running fan.

To resolve the problem, consider checking the relay for any visible damage, and contact a professional if necessary for replacement.

7. Other Reasons

Apart from the common issues discussed earlier, there could be additional reasons as to why your Honeywell thermostat's fan won't turn off.

These include: 

  • A blown 3A or 5A fuse in model-specific furnaces
  • Stuck high-limit switch
  • Tripped flame rollout 
  • Tripped low-pressure gas switch, 
  • Fan limit control issues in older furnaces 
  • Malfunctioning control board or relay
  • Faulty sequencer
  • Issues with the blower motor itself

Each of these problems may cause the blower in your HVAC system to continuously run, leading to unnecessary energy consumption and discomfort.

To address these more complex issues, it's highly recommended to consult a professional HVAC technician rather than attempting a DIY repair.

This ensures that your thermostat and furnace are properly diagnosed and safely fixed, preventing any further damage or potential hazards.

The Verdict

A constantly running fan might seem trivial at first but it can cause inconsistent temperatures, high energy bills, and unnecessary wear and tear on your HVAC system.

You can diagnose the thermostat but if the issue might be in the rest of the HVAC system, it’s best to get assistance from qualified technicians.

If you have any questions, don’t forget to leave a comment below, or check out the rest of our content from the home page.

Sources

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11 Comments

  • Frank
    Posted January 13, 2024 at 11:54 am

    New 3ton heat pump with electric strip. new T4. AC works with no problem. electric heat works no problem. in heat pump mode, it will reach thermostat setting, possibly 1 or 2 degrees above. once this happens the heat pump shuts off… but the indoor fan continues to run. It will run until the temperature drops in the house and the heat turns on again.

    I replaced the limit switch from 50-190 to 70-205, still same problem.

    one way to stop the fan is simply dropping the thermostat 1 degree. then the whole system will shut off. but once it calls for heat again, it will fall into the continuous cycle again. any idea? possibly a bad T4?

  • Renee
    Posted February 21, 2023 at 3:24 pm

    My fan never shuts off and there is no off switch under the fan setting -only auto or on – no matter if the heat is switched to off. My bills are high because the unit never shuts off-especially when I do not need anything in the early fall and spring or go out of town.

    • Daniel Walsh
      Posted June 1, 2023 at 11:29 am

      Hi Renee

      It’s likely that the issue you’re facing is related to a faulty thermostat or a wiring problem. When you set the fan to “auto,” it should only come on when the heating or cooling system needs to circulate air.

      You’ll need to inspect the wiring of your thermostat and HVAC system for any visible damage or loose connections or reach out to a professional technician to diagnose and repair the problem.

      Hope this helps

      Daniel

  • gale
    Posted April 23, 2022 at 7:26 pm

    Can.t get my fan to stay off!!!!!

    • Daniel Walsh
      Posted May 30, 2023 at 11:46 am

      I’d recommend checking if the fan is set to “On” instead of “Auto”. If it’s set to Auto and its set to a reasonable temperature, then there could be a wiring issue that would need to be investigated.

  • Mary Jo
    Posted April 8, 2022 at 10:21 pm

    I have a Honeywell home thermostat. Currently it is 100 degrees outside and although I have the A/C set for 78 the fan is running but the A/C is not. Therefore, I do not have a cool house, I have a hot, stuffy house because the fan does no cool it down. I cannot turn the fan off so just the A/C works. If i could dod that I would be happy. If I have to wait till the fan cools the house to 78 I will be in a hot house all night. Please help.

    • Daniel Walsh
      Posted May 30, 2023 at 11:41 am

      It appears that your Honeywell thermostat’s fan and A/C settings are not functioning properly. To fix this issue, first, ensure that your thermostat is set to “Cool” mode and the fan is set to “Auto.” If the issue persists, you may need to reset the thermostat by carefully removing it from the wall, taking out the batteries for 30 seconds, and then reinstalling it. If these steps don’t resolve the problem, you should consider contacting a professional HVAC technician to diagnose and fix the issue, as it may indicate a problem with the wiring or the cooling system itself.

  • Janet Young
    Posted April 8, 2022 at 3:47 pm

    My apartment complex uses their maintenance man to fix my A/C . He says that the fan will run by itself even when it’s turned off, and this is normal. He doesn’t know what he is doing.

    • Daniel Walsh
      Posted May 30, 2023 at 11:44 am

      While some thermostat models have a fan that runs continuously to maintain air circulation, the Honeywell thermostat should turn off the fan when your desired temperature is reached (if “Auto” is set).

      If the fan keeps running despite the system being off, it might indicate a wiring issue, or the fan setting is set to “On.”

  • Luther P Hinesly
    Posted March 23, 2022 at 12:08 am

    Put a new 5 ton Goodman Roof mount heat pump unit on with a Honeywell T4 pro thermostat and every time I plugged the thermostat on to its wall base, the fan would start. Unplugging the green wire from mounting base didn’t stop fan . Disconnecting the “C” wire from fan base and everything worked perfect.

    • Daniel Walsh
      Posted May 30, 2023 at 11:51 am

      Seems like there’s a wiring issue with your T4 Pro and heat pump unit that needs investigating. Best to turn off the power at the circuit breaker, and trace each wire from the thermostat to the heat pump to make sure they are going to the correct terminals. Also check for any loose connections, or damaged or exposed wires. If nothing obvious, then might be time to call in professional help.

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