Depending on how far north you live, your home heating system is imperative to your comfort and maybe even your safety. So having a furnace not turn on via the thermostat at the beginning of the heating season is, at the very least, alarming.

This article will cover several reasons why your furnace doesn’t turn on and provide you with a solution, so if you’re looking for a fix, keep reading.

6 Reasons Why Your Furnace May Not Turn on Via the Thermostat

There are a lot of working parts to your home’s HVAC system. In some cases, problems with certain components will stop your system from starting and/or running.

So even though the thermostat isn’t turning on the furnace, the problem may lie elsewhere. Having said that, we will address thermostat issues first.

Man In Front Of Thermostat That Is Not Turning On Furnace
Actually, the problem could be in another part of your HVAC system, not only in the thermostat.

1. Faulty or Incorrect Thermostat

Let’s start with the obvious.

The first thing you want to do is make sure your thermostat is set correctly. You have alternatives for Heat, Cool, and ON. Make sure you have it set to Heat.

This is a very common problem at the beginning of the heating season, especially if you also have central air.

Next, there could be problems with the thermostat itself, so check the following.

Solution. Many new thermostats require batteries, so ensure that your batteries are good. Using a battery tester is the best idea because you want to check for a voltage drop. The batteries may have enough power to light up an LED display but not enough to start your furnace.

Finally, make sure the type of thermostat you’re using is matched with your HVAC system since furnaces and thermostats aren’t mix-and-match.

There are three types of thermostats:

  • Low voltage
  • Line voltage
  • Millivolt

Low-end line voltage thermostats are the most common.

Low voltage thermostats operate under 30V and are direct wired. They’re most commonly used with:

  • Electric furnaces
  • Single-stage heating and cooling
  • Multistage heating and cooling

Line voltage thermostats operate between 120V and 240V and most commonly have single or double pole wiring. These are commonly used for:

  • Direct wired electric furnaces

Fortunately, most thermostats now come with a label identifying which types of systems they’re compatible with.

2. Faulty Wiring

There may be nothing wrong with your thermostat or your furnace, but with the wiring between the two.

To understand the connections between them, take a look at the video below.

Over time, your wiring can age and crack, fray, or connections can become loose. Any of these problems can break the connection between your thermostat and furnace.

Solution. If you’re able to inspect all wiring, make sure your connections are tight and replace anything necessary. You can use these troubleshooting tips if you feel up to the job. If not, call an HVAC professional.

3. Tripped Breaker

If you’re very fortunate, the reason your furnace isn’t turning on at the thermostat is simply because of the tripped breaker.

Solution: Check to make sure all your breakers are engaged.

4. Your Furnace Has Been Turned Off

In most cases, a furnace will have a dedicated power switch. It will either be on the furnace itself or a wall switch close to the furnace. Since this is something you wouldn’t typically turn on or off, you may not think of it.

Solution. Find the power switch and ensure that it’s on.

5. Airflow Issues

Your furnace—and your air conditioner—require sufficient airflow in order to operate. Without it, your equipment will eventually stop working, and your thermostat won’t be able to turn them on.

There are multiple causes for a lack of airflow. Here are some of the most common:

  • Dirty air filters
  • Damaged or obstructed ductwork
  • Improperly sized vents
  • Blocked or closed vents
  • Broken or dirty blower fan or motor

Solution. Dirty air filters are the number one cause of a multitude of HVAC issues so stay up to date with their maintenance. Either clean or change them in line with the manufacturer’s recommendations.

If you have an unfinished basement, at least some of your ductwork will be visible but a large percentage of it is typically behind walls. Over time they can form leaks or disconnect, and you can lose a considerable amount of airflow.

You can hire someone to come and inspect your ductwork or you can purchase an inspection camera and do it yourself. Amazon and most places like Home Depot will carry inspection cameras.

If your vents are improperly sized there’s not much you can do about that yourself, but you can ensure your existing vents aren’t blocked or closed.

Make sure any return air vents on walls aren’t blocked by furniture, and never entirely close any supply registers as either of these two things will significantly impact airflow.

Any long-term airflow issues will damage your blower motor as it works harder to push air through your system. Along with the issues mentioned above, be sure that you keep the blades of your blower fan clean.

Check the following video for a walk-through.

6. Problems with Blower Motor or Belt

Your blower moves both warm and cool air from your furnace and air conditioner respectively, but it also pulls air from your home. If your blower stops working, nothing will work.

So your thermostat and furnace could be in perfect working order.

If you’ve been hearing squeaking or screeching when your furnace was running, it could mean your fan belt is bad or the motor needs to be oiled. And just like the fan belt in your car, the belt on your blower eventually needs to be replaced as well.

Disassembling HVAC Blower Motor
The blower motor is the part of your HVAC system that gets your home to the temperature set on your thermostat.

Conclusion

As you’ve learned from above, if your furnace isn’t turning on via your thermostat, the reasons aren’t limited to the thermostat itself.

To recap, any of the following could be your issue.

  • Faulty or incorrect thermostat
  • Faulty wiring
  • Tripped breaker
  • Your furnace is off
  • Airflow issues
  • Problems with blower motor or belt

In some cases, your fix will be as simple as flipping a switch on a breaker or on your furnace itself. But with a little troubleshooting, you should be able to identify the problem.

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

Thank you for reading!