Furnace Turns On Then Off After A Few Minutes: Find Out Why

Have you found yourself in a situation where your furnace runs for a few minutes then stops? If yes, then you have a problem inside your furnace that needs to be fixed as soon as possible to keep your home warm. This is one of the problems that can occur and it is nothing new. This is also called ‘short cycling’. There are a few reasons why your furnace could be in short-cycling mode. In this article, we’ll talk about those reasons and how you can fix them. So, let’s start.

Why Does My Furnace Keep Shutting Off?

Why Does Furnace Turns On Then Off After A Few Minutes? If your furnace turns on then off after a few minutes, it’s mostly because of a faulty or dirty flame sensor rod, low airflow in the heat exchanger, a broken pressure switch, or the defective control board. To fix this issue, find why it occurred and try to repair or replace the faulty part.

To find out what is causing this problem, you need to open your furnace and inspect each of these parts in detail. Once you find it, it is very easy to fix the problem. Below we will go through all the possible reasons why this can happen.

5 Reasons Why Furnace Turns On Then Off After A Few Minutes

Possible Problem Solution
1. Dirty Or Faulty Flame Sensor RodClean up the flame sensor rod.
2. Low Airflow (Heat Exchanger Is Overheating)Try to cleandirty air filters or a dirty blower wheel.
3. Faulty Pressure SwitchUse the multimeter to measure if there is some problem with the pressure switch.
4. Faulty Draft Inducer MotorIt will need to be replaced if it turns out to be broken.
5. Defective Control BoardReplace the control board.

Each of these methods is explained in more detail below, so keep reading this article.

Also, if you are interested in How Much Electricity Does a Gas Furnace Use, feel free to read this article.

Finding The Source Of Problem

If you have a problem that your gas furnace shuts off after a few minutes, it is most likely a smaller problem that can be fixed in a day. On the other hand, if you already have experience in household chores, you’ll be able to fix this problem, but if you’ve never done DIY jobs, be sure to contact a professional.

When you work on a gas furnace, it could be dangerous not only for you but your whole family. Therefore, regular maintenance is essential. That way, you will ensure that your furnace is in good shape and will last quite a long time. The first step to solving this problem is finding the source of the problem. Below we will list the five most common causes.

5 Reasons Why Your Furnace Turns Off

If it happens to you that your furnace turns on then off after a few minutes, you must find the source of the problem. The typical problem why a furnace keeps turning off is because of one of these problems:

1. Dirty Or Faulty Flame Sensor Rod

Dirty Or Faulty Flame Sensor Rod

One of the reasons why your furnace turns off after a few minutes can be by a faulty or dirty flame sensor rod. This component of which the furnace is composed is here to keep an eye on the gas burner. A flame sensor rod is a safety device that is a built-in furnace to detect a flame. When it does not detect a flame, the gas valve is shut down. When the dirty flame sensor rod can’t sense the burner, the furnace first runs, then shuts off and starts again. This problem can be fixed very easily.

You can call a professional to help you fix this problem with your furnace. The way this problem can be solved is to clean the flame sensor rod with a lightly abrasive pad. In case that cleaning doesn’t help, then the flame sensor must be replaced with a new one.

Note! The problem is very similar for those who have an older furnace that comes with a pilot light. On this model, the flame sensor is over the pilot light (not on the furnace burners).

2. Low Airflow (Heat Exchanger Is Overheating)

Dirty Air Filters Cause Low Airflow

Another possible reason why your furnace may turn off immediately after turningiton is the low airflow. This is because the heat exchanger that is placed in the furnace can overheat if there isn’t enough airflow. Once the heat exchanger overheats (heats up to the maximum temperature), it activates the high limit switch to protect the furnace, and it shuts it down. If the high limit switch is broken (goes bad), then the furnace won’t turn off, and the heat exchanger will crack.

Here are also 3 most common reasons why low airflow may occur:

  • Dirty Air Filters. First, you must make sure that all of your air filters are clean. If you don’t replace your air filters every few months, the filters will become dirty and will make the heat exchanger retain heat and cause it to overheat. It is advisable to change your air filters every 90 days. With proper maintenance, you’re furnace will last longer.
  • Dirty Blower Wheel. Second, make sure to check the blower wheel. If the furnace turns on and off too quickly, the problem may be a dirty blower wheel. The blower wheel uses the blades to circulate air, and if there is dust, it won’t work as efficiently as it should. To prevent this, it is necessary to clean the blower wheel regularly.
  • Blocked Air Supply Vents. Lastly, check the air supply vents in your furnace to see if they are closed or blocked. All vents should be open (in all rooms). The heat exchanger can’t transfer the heat if there isn’t enough air. This can cause heat to build up and could potentially cause your furnace to short cycle.

3. Faulty Pressure Switch

Faulty Pressure Switch On Furnace

Another key reason why your furnace may turn on and off after only a few minutes is because of a faulty pressure switch. The role of the pressure switch is to ensure that ignition is safe by closing with airflow from the draft inducer motor that is going through the burner. If the switch is faulty, it will not notify the ignition. Ignition will be paused after a couple of minutes, which will result in turning off the furnace. By using the multimeter you can measure if there is some issue with the pressure switch.

4. Faulty Draft Inducer Motor

Faulty Draft Inducer Motor on Furnace

This problem is related to the previous one and can be said that a faulty draft inducer motor is connected to a faulty pressure switch. The main role of a draft inducer motor is to draw air into the furnace burner and then out to the flue. The pressure switch closes and activates the ignition process. If the draft inducer motor is broken, it will not work correctly and close the pressure switch and ignite the furnace. For that reason, the furnace will only run for a few minutes and then turn off.

5. Defective Control Board

Defective Control Board On Furnace

Every furnace comes with a control board that main task is to supply power to all inner workings of the furnace. If something inside your furnace is defective or broken, the furnace may start to turn on and off. Without a control board, you can’t run the furnace. If it turns out that your control board is broken, it won’t be a simple fix. You will need to replace the control board in order to fix your furnace.

Other Possible Reasons Why Your Furnace Turns On And Off

If you’re still having a problem with your furnace, take a look at the following issues:

  • Blower Motor Does Not Work

The blower motor is in charge of keeping the air circulating in your house. Sometimes it can happen that your furnace runs even when the blower motor is turned off, but that’s rare. The way you can check that this is the case is to hold your hand near the vents. If you notice that air is coming out then the blower motor is working, but if there is no airflow, the blower motor is most likely the problem.

  • Flue Pipe (Exhaust Vent)

The flue pipe that is located on the house roof can also be the reason why your gas furnace shuts off after a few minutes. This is because the dirt, sticks, leaves, or animal nest ends up inside the pipe which can cause the blockage. Blockage then causes hot gases to build up in your furnace which leads to overheating. Furnace has built-in safety features that can trigger your furnace to turn off when it gets overheated.

  • Problem With Over-sized Furnace

Although it is very unlikely that your furnace is too big for your house, this can also cause that your furnace turns on and then off. In this case, you’ll need to replace your furnace with a new one. When your furnace is too big for your home, then your house will heat up quickly and then the furnace will turn off.

Final Thoughts

When your furnace turns on and then off after a few minutes, that is something that should not ignore. As soon as you realize that this is the problem, we advise you to contact a professional HVAC engineer. This way, you will prevent a much bigger problem or even the replacement of your entire system, which will ultimately cost you a lot more. It is therefore advisable to do the regular maintenance of your HVAC system to prevent this from happening. I hope this article helped you, and if you have additional questions, feel free to contact us.

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