Thermostat Won’t Turn On? Try These 7 Quick Fixes

Thermostat Won't Turn On

Got a thermostat that won’t turn on? Either itself or perhaps your furnace or air conditioner?

A broken thermostat is basically the same as having a broken air conditioner or furnace – so this is a big deal! Thankfully, it can often be caused by several common issues.

In this article, I’ll go through all the possible reasons and fixes for thermostat issues.

Why Your Thermostat Won’t Turn On

In short, a thermostat may not turn on due to needing new batteries, a tripped circuit breaker, or a loose wiring connection.

While it is more common that a thermostat not turning on is simply a symptom of something going wrong with another component of your HVAC system, there are a few things that can stop your thermostat itself from working.

1. Dead or Dying Batteries

If the LED screen on your thermostat is blank this is a pretty good indication that you have dead batteries. However, even if the screen is lit, there still may be an issue with batteries.

In order for your thermostat to start your furnace, air conditioner, humidifier, blower motor, or any other component of your system the batteries need to have sufficient voltage. And that’s significantly more voltage than your LED screen will take.

Solution. The best thing to use is a battery tester if you have one. If Not, simply change out the batteries and see if that corrects your problem.

Hand Holding Thermostat With New Batteries
Lack of battery power is the most common problem, as well as the easiest to deal with.

2. Tripped Breaker

Some thermostats only use batteries as a backup in order to save their programming in case of a power failure.

In this situation, if the breaker that your thermostat is on has tripped, then your thermostat is inoperable.

Solution. If you’ve already checked to ensure the batteries are not the problem, then check your breaker. If one is tripped, simply reset it. However, it’s a good idea to find out what it is that caused the breaker to trip in the first place – and solve the root cause.

3. Faulty or Broken Thermostat

It may be that you just need to replace your thermostat.

Thermostats typically have a lifespan of around 10 years so take that into consideration if you’re having problems.

If you had any of the following issues leading up to the thermostat simply not working, a dead thermostat may be your issue.

  • Your HVAC has been turning on and off
  • Your thermostat readings have been incorrect
  • Constant temperature shifts
  • Your thermostat failed to respond when you changed settings

Solution. If you’ve determined that it’s time to buy a new thermostat, here are some newer features to consider:

  • Smart or learning thermostat
  • Auto changeover
  • Control
  • Automatic temperature changes
Man Using Multimeter To Measure The Thermostat Conductivity
Thermostats normally have a 10-year lifespan, so it may be time to replace yours.

4. You Have the Wrong Thermostat

If you’ve recently replaced your thermostat, this could be your problem.

Thermostats need to be matched to your heating system so if you haven’t installed the correct type for your system the thermostat and your HVAC components cannot communicate with each other—or the system will fail completely.

There are two types of thermostats most commonly used in HVAC, a line voltage or low voltage thermostat.

  • Line-voltage thermostats. These are typically used in heating systems such as radiators or electric baseboard heating. This type of thermostat operates on 240V or 120V.
  • Low-voltage thermostats. Low-voltage thermostats operate at 24V and are typically used for central HVAC systems that use either electricity, gas, oil, or heat pumps. These can also be double or multistage systems.

Why Your HVAC Equipment Isn’t Turning Your Thermostat On

As mentioned, issues at the thermostat are most often caused by issues with one or more of your HVAC components. Your:

  • Furnace
  • Air conditioner
  • Blower

Let’s look at the specifics of why any one of these could impact your thermostat.

Remember, your thermostat is a communication device. It sends a message to your furnace, air conditioner, or blower, and if it doesn’t get the right response your thermostat will not turn on.

1. Clogged Air Filter

Lack of air filter maintenance is one of the most common causes of HVAC issues since lack of airflow can destroy your system.

Most furnaces have a safety feature that will stop them from turning on if there are serious airflow issues such as a clogged air filter or drain issue.

Solution. Follow the maintenance schedule recommended by your air filters manufacturer. However, depending on your household, you may have a little leeway.

You may not need to change your filter as often if:You have a small household of one or two people, and you don’t have any pets.
You will likely need to change your filter more often than is recommended if:You have a larger family and multiple pets

2. Clogged Condensate Pan or Drain

If it’s the cooling season and your thermostat won’t turn on your air conditioner, your drain pan may be full. This is from moisture that collects and drains from the warm air your air conditioner pulls from your home.

Solution. Check to see that the float switch in the pan is working properly and look for a clog in the drain line.

Check out the following video for steps on cleaning your condensate line.


There are a few reasons why your issues may be directly related to your thermostat, but there’s also a good chance your problems lay with your HVAC equipment.

To recap, check the following:

Issues directly related to your thermostat include:Dead or dying batteries
Tripped breaker
Faulty or broken thermostat
The wrong type of thermostat
Issues related to your HVAC equipment:Clogged air filters
Pilot light issues
Clogged condensate pan or drain

Hopefully, this information has helped you detect or diagnose the problem with your thermostat.

While you’re here, why not check out our related posts below, perhaps we can help you with something else.

Thanks for reading.

I've been helping homeowners with appliance repair since 2016. Starting out as an enthusiastic amateur, I've since worked with many Appliance, HVAC, and DIY experts over the last 7+ years. My mission is to help fix your appliances and prevent future issues - saving you stress, time, and money. Visit my author page to learn more! Read more