Furnace Constantly Running? 5 Fixes to Stop Burning Money

Furnace constantly running

Is your furnace constantly running?

You’re not alone! I understand how frustrating it can be when your furnace won’t stop running, especially when you’re trying to save on energy costs.

Luckily, you’ve come to the right place to fix the issue.

If your furnace is constantly running, you’ll need to check the thermostat, replace the air filter, and inspect the ductwork. If the issue persists, please examine the limit switch and consider the size of the furnace.

Read on to keep your furnace from constantly running!

Furnace Won’t Stop Running? Try These 5 Fixes

If one of the components in your furnace malfunctions, it could cause the unit to run continuously. But don’t worry! In this section, I’ll guide you through five different solutions you can try.

Keep in mind that fixing the problem will probably require accessing internal parts, so having the manufacturer’s manual handy is essential.

Can’t find your manual? No problem! Click the link below to learn how to find any product’s manual online.

Are you ready? Let’s get started!

#1 Check The Thermostat

I find that when a furnace won’t stop running, it’s typically due to an issue with the thermostat.

If the thermostat is set to a very high setting, your furnace will run continuously trying to reach the desired warmth. Therefore, it’s important to ensure you’ve selected the correct temperature.

Thermostat settings
Make sure you’ve selected the correct thermostat settings.

Additionally, some thermostats come with a fan option. If yours has this feature, please double-check that the “ON” mode is not activated. When in “ON” mode, the blower fan will run continuously, even when the furnace is not heating.

However, if you’ve selected the correct settings, but your furnace is still running, then there’s a good chance that the thermostat is faulty.

You see, a malfunctioning thermostat won’t accurately read the room’s temperature. As a result, it will keep signing the furnace to run, even if the room is already at the desired temperature.

In such cases, you’ll need to replace the thermostat. Here’s how to do it:

  1. Turn off the power at the circuit breaker and remove the thermostat’s front panel.
  2. Take a picture of the wiring connections for future reference.
  3. Carefully disconnect the wires from the old thermostat and undo the screws holding the mounting plate in place.
  4. Secure the new mounting plate and connect the wires to the new thermostat. Remember to use the reference picture you took earlier. It’s also important to read the manufacturer’s manual for guidance.
  5. Place the front panel in place and restore power.

Once you’ve replaced the thermostat, please test it by adjusting the temperature. If the issue persists, you’ll need to check the air filter. Read on to learn how to do it.

#2 Replace The Air Filter

In my experience, a dirty or clogged air filter can also cause the furnace to run continuously.

The air filter traps dust particles, dander, and other allergens before entering the unit. However, when the filter gets clogged, it can restrict airflow and cause your furnace to run longer to reach the desired temperature.

dirty air filter
Is your furnace constantly running? Check the air filter!

Luckily, cleaning or replacing the air filter in your furnace is very simple. You’ll just need to:

  1. Turn off your furnace and remove the panel to access the air filter. It’s typically located on the vent, but please read the owner’s manual, as the exact location can vary depending on your furnace’s model.
  2. Slide out the filter from its slot.
  3. If your furnace has a reusable filter, please clean it. You can use a vacuum or rinse it with water. Then, let the filter air dry.
  4. If you have a disposable filter or notice any signs of damage, you must get a replacement.
  5. Install the filter. Make sure it’s facing the correct direction.
  6. Turn your furnace back on.

Please keep in mind that you should replace the air filter every 1 to 3 months to prevent different performance issues.

#3 Inspect the Ductwork

Unfortunately, ductwork issues can also explain why your furnace is constantly running.

The ducts and vents transport air from your furnace throughout your home and circulate it back. When there’s an obstruction, your furnace has to work harder to push air through the system, leading to longer running times.

Therefore, it’s crucial to inspect the ductwork. Look for any obvious signs of damage, such as cracks, loose ducts, or rust. If you notice any gaps or leaks, please seal them, as air leaks can also cause your furnace to run for longer periods.

Keep in mind that diagnosing and solving ductwork issues can be a bit tricky. Therefore, if you’re not an experienced DIYer, you should call a licensed HVAC technician.

Tip: Consider scheduling annual maintenance for your furnace to ensure its effectiveness and prevent ductwork issues.

#4 Examine The Limit Switch

If you’re still struggling with a furnace that won’t turn off, there’s likely an issue with the limit switch.

The limit switch is responsible for monitoring the temperature of the air passing over the heat exchanger. If it senses that the furnace is overheating, it will turn off the burners to prevent performance issues and accidents.

However, if the limit switch is faulty, it won’t sense that the furnace is getting too hot. As a result, it will fail to turn off the unit when necessary, and your furnace will continue running.

To check the limit switch, you’ll need to:

  1. Turn off your furnace and close the gas valve.
  2. Remove the top cover panel and access the limit switch. For detailed instructions on how to access the limit switch, please refer to the owner’s manual.
  3. Take a picture of the wiring connections for future reference. Then, carefully disconnect the wires.
  4. Remove the limit switch from the furnace.
  5. Set your multimeter to the lowest ohms of resistance. Then, touch the probes to each terminal.
  6. If the multimeter shows no continuity or infinite resistance, you’ll need to replace the limit switch with a new, compatible one.
If you prefer to watch, here’s a video that provides step-by-step instructions on how to test and replace a gas furnace limit switch.

Remember that it’s best to call a professional if you’re uncomfortable testing the furnace components yourself.

#5 Check the Size of the Furnace

If you’ve tried all the fixes above, but your furnace keeps running, it is probably too small for your home.

You see, if the furnace is too small, it will need to work harder and run for longer periods to reach the desired temperature, especially during winter.

In such cases, the best solution is to replace the furnace with a new one that matches the heating requirements of your space. If necessary, please consult an HVAC technician to ensure you purchase the right furnace.

Wrapping Up: Fixing Constant Furnace Running

That about covers it! Hopefully, now you know why your furnace is constantly running.

Remember, to fix the issue, you’ll need to make sure you’ve set the correct settings in the thermostat and turn off the fan feature. It’s also important to clean or replace the air filter and inspect the ductwork.

Don’t forget that if the problem persists, you’ll need to test the limit switch and check the size of the furnace.

Thank you so much for taking the time to read this post. If you’ve found it helpful, please check out our other related articles.

Good luck!

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