Reasons Why a Humidity Sensing Bathroom Fan Won’t Turn Off

The primary purpose of having a humidity sensing fan in your bathroom is to help remove excess moisture from the air. This helps prevent damage to the wall, ceiling, and the growth of mold and mildew in your bathroom.

But what happens if the fan keeps running all the time? What happens when it won’t turn off?

The main reason why your bathroom fan keeps running could be that the humidity sensor is defective or not adjusted properly. It could also be that the fan was made to run continuously.

And you don’t want a constantly running fan. It can become a fire hazard, damage your fan, and put the lives of your loved ones at risk.

In this post, we discuss why your humidity sensing bathroom fan won’t turn off and how you can fix the issue.

Reasons Why Your Bathroom Fan Won’t Turn Off

1. Faulty Wiring

If your bathroom fan has faulty wiring, it won’t turn off however much you try. This problem can result from soothing as simple as a loose connection.

The issue can also occur if the connection was not made in the first place.

One thing to note is that a bathroom fan that runs non-stop isn’t caused by the fan’s wiring. This is because if the fan’s wiring were the problem, the fan wouldn’t turn on at all.

2. Malfunctioning of Humidity sensors

Malfunctioning of humidity sensors is the most probable reason your humidity sensing bathroom fan won’t turn off.

You need to know that these humidity sensors come specifically designed to turn the fan on as soon as the air reaches a specific humidity level.

In case of a malfunction, your fan will run continuously.

Also, if your bathroom is one of those that are ever humid, the sensor can make your fan run at all times.

3. The Fan was Designed to Run Continuously

Do you know that some humidity sensing bathroom fans are designed to run all the time? It does not matter whether your bathroom is humid or not.

These fans run quietly and use less electricity.

To tell whether you have a continuous humidity sensing bathroom fan or one that is malfunctioning, check your electricity bill and see whether there are noticeable differences.

The noise level can also help you confirm the nature of the fan.

4. Issues with the HVAC

If your home has an HVAC system, an override control needs to be in place as well. An override control is specifically designed to be accessible to the homeowner to help them shut off all fans and other aspects of the HVAC.

Override controls are usually installed on a wall near your home’s thermostat or electrical breaker panel.


Reasons Why a Humidity Sensing Bathroom Fan Won't Turn Off

1. Replace the Wiring

To replace your fan’s faulty wiring, get an electrician. However, if you’re really good at electrical work, you can complete the task independently.

To get the wiring in order, you need to:

  • Check the switch box to locate the wires going to your bathroom fan, and use electrical tape to mark them.
  • Remove the fan from the ceiling, the cover plates, and un-attach all the wires connected to it. Note that this process might require you to enter the attic.
  • Pull out all your bathroom fan’s wiring from the switch box – ensure that you remove all taped wires.
  • Use the old wire to determine the length of the wire you’ll need. Cut the new wire to length.
  • Feed the new wiring from the switch box to the attic.
  • Get back into the attic and connect the new wiring to your fan and switch box.
  • Check to ensure that everything is connected correctly and turn the power on to test the new wiring.

2. Replace the Humidity Sensor

If you’re sure that your fan’s humidity sensor has a malfunction, get a replacement. These sensors are very easy to install. You actually only need a flatbed screwdriver to complete the task.

The first thing you need to do is make sure that the power to your bathroom is turned off. You can then use a voltage tester to ensure that it’s safe.

To replace the humidity sensor, you should:

  • Take out the screws to remove the sensor from the wall.
  • Take off the faceplate using a screwdriver – You’ll see the screws connecting to different wires.
  • Remove the screws and remove the old humidity sensor.
  • Follow the user manual to reconnect the wires to the right screws and then put everything back together.

3. Reset the HVAC Override Control

If you have issues with the HVAC override control, you can choose to either get an HVAC technician or rest the override control on your own.

To do so, shut off the power to your bathroom fan, turn off any circuit breaker relating to the HVAC unit and then wait for 30 seconds before turning everything back on.

This reset method is easy to do and most likely fix the issue. However, if the fan isn’t fixed even after the reset, it’s high time you contacted the technician.

Frequently Asked Questions

Q. Why does my bathroom fan keep turning on?

The most common reason your bathroom fan keeps turning on is that it’s connected to a humidity-controlled switch. Therefore, whenever the humidity level in the bathroom rises to a set point, it turns on automatically.

Q. How long does it take for a bathroom fan to turn off?

The fan usually stays on for 20 seconds – 20 minutes. However, you can decide how long you want the fan to keep running – ideally, until all the moist air is gone.

Q. How do you adjust a humidity sensor switch?

To adjust a humidity sensor switch, turn the dial clockwise. This will increase the sensitivity for the device to respond faster.

Q. Should a bathroom fan run all the time?

Experts advise that you shouldn’t leave your fan to run all the time. Let it run for at most, 20 minutes during and after bath. Running the fan for too long can become a fire hazard.

Q. What humidity level should my bathroom fan be set at?

Unless you have special humidity conditions in your bathroom, always set the humidistat on 60%.


A humidity sensing bathroom fan does more than prevent your bathroom mirror from getting foggy. It removes moisture from your bathroom and prevents bigger problems like peeling paint, rotten window frames, and wood decay inside walls.

Ensuring that the fan runs correctly should be your number one concern if you want to keep the bathroom in good shape and prevent risks of fires, among other things.

We hope that you’ve learned a lot from this guide and you’ll be able to deal with the fan should it misbehave again.

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