How to Tell if Your Furnace is Short-Cycling & What to Do

feeling chilly due to short cycling furnace

The chill in the air signals that winter is just around the corner. The temperature outdoors will soon fall to uncomfortable levels. Ensure that your family does not have to suffer from frigid nights. Check your heating system before winter arrives to make sure that it is in excellent condition. Some problems might require simple and basic fixes. However, some need to be corrected by a professional HVAC technician. This includes furnace short cycling or when your furnace runs then shuts off and starts again in quick successions.

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How To Tell If Your Furnace Has A Short-Cycling Problem

Furnaces operate by providing heat in a home until the set temperature is reached. After that, it will turn off until the level of heat declines again. This process usually takes a while, so the furnace doesn’t need to turn on again so soon. However, if a furnace short cycles, it will turn on and shut off repeatedly and quickly. The desired temperature will not be reached, and the constant turning on and off will wear out the system. As a result, your house will remain cold and uncomfortable even though the furnace is running continuously.

What Does A Furnace Short Cycle?

question asking why does a furnace short cycleA short cycling furnace must be fixed immediately. This issue consumes a lot of energy and does not heat your home correctly. Not only that, but it also damages parts of your furnace. Make sure to have the problem resolved as soon as you notice it.

Various reasons can cause short cycling. The corresponding solution depends on what is causing it. Below, we discuss some cause for short cycling:

Furnace Is Overheating

Heating and cooling systems have built-in safety precautions to protect it from damage. Furnaces can get too hot. When the temperature reaches a dangerous level, the unit will switch off automatically. This way, damages are prevented.

Overheating can cause cracks in the heat exchanger. In turn, lethal carbon monoxide can leak through these cracks. Overheating is typically caused by dirty air filters and blocked vents.

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Clogged Furnace Filter

image of a furnace filter replacement

The filter’s job is to block impurities from entering your HVAC system and house. Over time, the filters become clogged with these contaminants. When this happens, the furnace will run for several minutes then shut down. The clogged filters prevent proper airflow as well. This will make it hard for your furnace to cool down. Heat in your furnace will build up until it reaches a certain level. Your furnace will switch off automatically as a safety measure. Make sure to wash your filter or replace it if you have disposable ones.

Something Is Blocking The Exhaust Vent

The exhaust vent should remain open at all times. However, the vents can sometimes get blocked. Shrubs nearby might have grown too large, or snow might have piled up. Cut all nearby vegetation and remove the snow. Animal homes, such as beehives and nests, can also sometimes cause blockages. Call an animal control expert to help you remove all dangerous animals from blocking the vents.

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The Thermostat Is In The Wrong Spot

image of person adjusting thermostat to turn on furnace

The thermostat has sensors that help determine the indoor temperature. This allows it to regulate the furnace as per what it gauges in the environment. If it is in the wrong spot, it won’t be able to do this properly as the sensor readings will be inaccurate.

Ensure that the thermostat isn’t placed near any heat sources like a heating grate or a sunny window. Nearby heat sources can make your thermostat think that it has reached the set temperature and it will prompt the system to shut down. Placing it in a neutral spot will ensure that the thermostat’s temperature readings are not influenced.

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Blocked Heat Grates

The warm air is released into your house via the grates. Having blocked heat grates means that the air gets trapped inside your furnace instead of being circulated throughout your home. Your system will overheat, and this will lead to short cycling. The dampers control the grates. These allow you to open and close the grates so that you can choose whether to heat the room or not. This allows your home to be more energy-efficient. However, at least 75 percent or more of the grates should be open at all times to avoid furnace overheating.


Faulty Flame Sensor

The flame sensor monitors the gas valve. Its job is to shut the valve when there is no flame and keep raw gas from circulating throughout your home. A faulty flame sensor closes the gas valve even when needed, so the flame turns off as soon as it is lighted. The flame sensor might need cleaning. Call an HVAC tech to schedule a furnace tune-up or a furnace repair.

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Incorrect Furnace Size

A furnace that is too large for the space it needs to heat will lead to short cycling. It will consume a lot of energy to heat your home. This leads to irregular heat distribution throughout your home. Unfortunately, this will lead to worn down components, high heating bills, and more pronounced temperature swings. The only solution to this is to invest in a furnace that is the correct size. An expert HVAC technician can perform the Manual J Load calculation to find the right size, make, and model for your home.



Furnaces keep your home safe and warm during the cold season. A short cycling furnace needs to be fixed immediately. Find the cause using the clues listed above. Do not hesitate to contact your local trusted HVAC technician to diagnose and repair your furnace. This way, you can enjoy a warm, safe, and stress-free winter.

Call Wilcox Energy For All Of Your HVAC Requirements

Wilcox Energy offers high-quality heating and cooling services all throughout the southern Connecticut shoreline. We hire only professionally certified technicians who can assist you with all of your HVAC needs. Some of our services include furnace maintenance, boiler repair, AC installation, ductless system replacement, and much more. Our HVAC contractors have years of experience and extensive knowledge to conduct accurate services.

Rest assured that our company has affordable heating and cooling rates in the area. Our tune-up services can improve your home comfort, energy efficiency, and cost-effectiveness. We can also recommend you with the most suitable HVAC make and model within your budget should you need to replace your current unit. Your satisfaction with our work is important to us. That is why all our works are guaranteed. Schedule an appointment with us and call Wilcox Energy today. We provide free, no-obligation, in-home consultations.

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For more information about our HVAC services, be sure to contact Wilcox Energy. You can click here to contact us, or you can call us at (860) 399-6218 to find out more. We offer a full line of heating and cooling repairs, maintenance services, and installations.