Furnace Is Clicking Off And On – What Could Be Wrong?

It's no secret that a properly functioning furnace is essential to keep your home warm. However, if your furnace is clicking on and off, it's a tell-tale sign that it isn't running efficiently. So, when this is happening, what could be wrong with your furnace? We have researched to help answer that question for you in this article!

If your furnace is clicking on and off, then it could be due to the following:

  • Clogged Fan Shafts
  • Low Airflow
  • The furnace is Short Cycling
  • Defective Thermostat
  • Clogged Inducer Blowers
  • Worn Out Bearings and Belts
  • Faulty Blower Motor
  • Worn Out Fan Belt
  • Broken or Jammed Gas Valve
  • Dirty Flame Sensor
  • Old Furnace
  • Faulty Electric Components

There are a lot of components that need to be up to par for your furnace to run correctly. With that, it is essential to understand why each of these culprits could cause your furnace to click on and off.

That's why in this article, we explain each in detail to help you pinpoint the issue. In addition, we will discuss how often you should change your furnace filter, so read on!

Fixing a gas furnace, Furnace Is Clicking Off And On - What Could Be Wrong?

Top Reasons Why Your Furnace Is Clicking Off And On

A furnace is a device that heats water, air, or the atmosphere to provide warmth in a building. A furnace has one or more fans that circulate the air and a heat exchanger.

The air enters from outside through an opening in the wall and is then heated by the heat exchanger and blown into rooms of the house.

However, a furnace can't do its job if it keeps clicking on and off. So what could cause this issue? Let's take a look at the most common culprits!

Digital termostats

Clogged Fan Shafts

A clogged fan shaft reduces airflow, which causes the blower motor to cycle more frequently on and off.  To clean a clogged fan, turn off your furnace and wait until it cools completely.

Unscrew the casing of your furnace to expose the fan shaft. Remove any debris found at the bottom using tools such as scraping knives or screwdrivers.

Once you have removed all items, spray the shaft with a lubricant such as WD-40. Tighten the casing of your furnace back up after applying the lubricant to ensure proper functioning.

Low Airflow

When there is not enough airflow, the blower motor switch will turn on and off frequently to try and push more air through. However, the safety limit of high voltage overload can cause the switch to trip and turn off the power.

A clogged air filter can also cause low airflow. Therefore, it is recommended to clean or replace the filter every often to ensure proper servicing of your furnace.

The Furnace is Short Cycling

Short cycling means that when your furnace isn't running correctly, it will turn on and off frequently. This is most common when there are problems with the thermostat.

Over time, you may notice that there are times when your furnace turns on and off at the same temperature. If this is happening, it could be because of a defective thermostat.

Defective Thermostat

A broken thermostat will cause your furnace to run inefficiently or turn on and off frequently to try and reach the set temperature.

To test if you have a defective thermostat, set the temperature to low and wait 10 minutes. If your furnace turns off but comes back on within 5 minutes, then you likely have a defective thermostat.

Clogged Inducer Blowers

The inducer blower is responsible for pushing air into the furnace, which helps push warm air out of vents. If the inducer blower gets clogged, your furnace will click on and off at the same temperature.

To fix this, turn off your furnace and wait for it to completely cool before attempting any repairs. Next, unplug the inducer blowers by pulling them out of their sockets. Finally, remove dust or debris using a vacuum cleaner, screwdriver, or a piece of wire.

Worn Out Bearings and Belts

As you use your furnace, the bearings and belts wear out over time which could cause the blower motor to turn on and off frequently. This is often caused by insufficient lubrication but can also be due to a faulty belt or worn-out bearing.

To find out if the belt is defective or worn out, turn your furnace on and run through a complete cycle (turning off at set temperature). If there is a burning smell during the furnace's operation, then your belt is likely damaged and should be replaced as soon as possible.

If you notice any grinding during the cycle, your bearings might be worn out and need to be replaced.

Faulty Blower Motor

To function, your furnace blower motor needs electricity. If there is a problem with the wiring, the motor could become damaged and will, in turn, cause your furnace to click on and off frequently.

Worn Out Fan Belt

If the fan belt on your furnace is defective or worn out, then it will cause your blower motor to turn on and off frequently. If this happens, you should replace the belt as soon as possible.

Broken or Jammed Gas Valve

The gas valve of a furnace heats up to allow the flow of gas through to the burner. If this valve gets jammed or broken, then the flame signals from your thermostat will not reach it, and your furnace will turn on and off frequently.

To fix this issue, shut off the electricity powering your furnace at the breaker box. Next, unplug the furnace from its power source. Once this is complete, you can remove the gas control valve and examine it for issues.

Dirty Flame Sensor

The flame sensor has two probes that allow it to sense the presence of a flame. If this sensor gets dirty, the machine will turn on and off excessively to reach the set temperature.

To clean it, unplug your furnace before removing any panels. Then, use compressed air or alcohol wipes to clean the sensors.

You May Need a New Furnace

If the above solutions do not fix your furnace from short cycling, you may need a new furnace. This is more likely if your system has been in service for over 15 years or if you have had any problems with your furnace in recent years.

Faulty Electrical Components

Technician repairing furnace

Some symptoms of a faulty electric component include:

  • An orange glow from the burners when the furnace is not heating.
  • A burning smell is coming from your vents during operation.
  • Noisy or rattling sounds are coming from your fan blower motor.

If you notice any of these symptoms, you likely have a faulty component in your furnace.

How long does a furnace inducer last?

On average, a furnace inducer will last 15-20 years.

If your blower turns on and off frequently, you may have a faulty blower motor. This could be caused by insufficient lubrication or worn-out bearings.

If your furnace inducer is over 15 years old and has these issues, it may be time to replace it.

What causes inducer motor failure?

A furnace inducer motor turns the air blower which then blows warm air into your home. It's located in the return duct and services one heating zone (typically for smaller homes).

Typically the inducer motor of a furnace will fail due to insufficient lubrication or worn-out bearings from old age.

How often should you change furnace filters?

How often you should change your furnace filters will depend on the type of filter you have. For average-sized furnace filters, they should be changed every three months. Thicker furnace filters (3-4 inches) are typically changed every six to nine months.

Lastly, thick furnace filters (6 inches) are changed about every year. However, you can always clean your air filter every month if you have a lot of pets in the home to keep air flowing properly.

Furnace filter

Should you clean your furnace blower?

It is not recommended that you clean your furnace blower yourself. Cleaning it can be hazardous and cause severe damage to your system if done incorrectly. Instead, it is recommended to have a professional clean your furnace blower yearly.

How do I check my furnace spark ignitor?

The best way to see if your furnace spark ignitor needs replacing is to turn the power off to the furnace. Next, remove the front housing of your furnace and check for damage or wear on it. If you notice any issues with the electrical connectors, then it's time to have them replaced.

If you do not find anything wrong with your spark ignitor, then you may have an issue with the automatic air vents in your ductwork.


Final Thoughts

Overall, diagnosing why your furnace is clicking on and off can be challenging to do independently. The best thing to do is to contact a professional to assess the issue. Take a look online for reputable HVAC companies, or ask a friend if they know someone they trust to help with your problem.

If you liked this article, then you should also check out:

How To Turn An Old Floor Furnace On And Off

How To Relight Furnace Pilot Light?

How To Make A Pellet Stove Burn Hotter

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