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Is Your Furnace Short Cycling? Here’s What to Do

There’s nothing like a cozy and comfortable home during the cold winter months. But keeping your home warm when the temperatures drop below freezing takes a toll on your furnace. It can even cause the system to become inefficient and develop mechanical issues if proper care and maintenance are not taken into account. 

A typical problem with your furnace is short cycling or overheating. Short cycling refers to the start-and-stop cycle that keeps the furnace from properly heating your home. 

So what causes short-cycling furnaces? Can it be remedied? Here are some things you should know about short-cycling heating systems.


It’s a complex question: “Why is my furnace short-cycling?” However, some common problems result in short cycling, such as an overheating system. If your furnace starts to overheat, it may shut off to prevent further damage. 

Overheating can also potentially create cracks in your heat exchanger, which could lead to dangerous carbon monoxide leaks in your home.

What to Do: Contact your local heating specialists to have them repair your unit according to its specific needs. When your furnace is working properly, you shouldn’t have to worry about overheating.

Thermostat Problem

If you have a short-cycling heater, turn next to your thermostat.

A broken or poorly placed thermostat is one of the leading causes of short cycling in furnaces. You may also want to rethink the location of your thermostat. Ideally, a thermostat that is placed too close to a heat source or in direct sunlight tends to warm up too quickly. This signals your furnace to shut off before your home is adequately warmed.

What to Do: Don’t place your thermostat directly over a heat register or near a drafty door or window. Test the unit regularly to ensure it is working optimally. Is your thermostat mounted in the wrong place? You can choose to either relocate the thermostat yourself or reach out to a professional for assistance.

Age-Related Problems

Maybe unsurprisingly, a short-cycling furnace can be linked to old age.

Your furnace’s efficiency tends to decline with age. An old and faulty furnace will short cycle more often and fail to warm your space adequately. Like all the other devices in your home, a furnace is subject to regular wear and tear, which becomes more pronounced with age.

What To Do: Wait until the furnace exhausts its usefulness due to advanced age before you act. Even if your old furnace has no significant mechanical issues, update it with a newer version that provides better performance and is more energy-efficient.

Dirty Air Filter

Dirty air filters restrict airflow and cause pressure to build up inside your system. The blocked air in the furnace, in turn, raises internal temperatures causing the unit to shut off automatically.

What to Do: Replace your air filters regularly, at least once each month, to prevent blockages and restricted airflow that leads to short cycling. You should also schedule frequent cleaning and maintenance to avoid clogged air filters.

Oversized Furnace

Have you checked the potential causes above but still find yourself asking, “Why is my furnace short-cycling?” If your furnace is short cycling with a new filter, an oversized furnace may be to blame. A heating system that’s too big for your home is one of the most common causes of short-cycling furnaces.

An oversized furnace that doesn’t match your home’s size may heat your small spaces quickly but unevenly. Such furnaces will short cycle rapidly with the rising temperatures in your home. Also, households with poor insulation may experience rapid short cycling. In this scenario, the furnace could be producing adequate heat, which is then lost through faulty seals, holes, and cracks.

What to Do: Install an appropriately sized furnace for the size of your home to avoid a short-cycling heater. You should also insulate your areas adequately to prevent energy loss.

Bad Flame Sensor

If you have a short-cycling furnace, you may be dealing with a malfunctioning or dirty flame sensor. When you have a bad flame sensor, your furnace flame will shut off right after lighting. If your furnace turns off after two to 30 seconds, this may be because your malfunctioning flame sensor cannot detect the heat created by the furnace. As a result, the gas valve closes and shuts off your furnace.

Although a malfunctioning flame sensor may shut off the gas at the wrong time, you shouldn’t feel too frustrated about this problem occurring. Flame sensors are safety devices that are simply trying to ensure that gas doesn’t enter your home and put your health at risk. If you’re experiencing this issue, rest assured that it’s nothing a professional HVAC technician can’t fix.

What to Do: You’ll need to either clean or replace your flame sensor with the help of a professional technician. A replacement will be needed if the sensor is broken or cracked.

Malfunctioning Blower Motor

While less common, a problem with the blower motor can cause a short-cycling furnace. The blower motor works by pushing air through your heating system and sending it out into your home. However, when the blower motor malfunctions, the warm air that’s generated will collect inside your furnace with no way of escaping — causing the furnace to turn off for safety reasons.

When it comes to a furnace blower motor, it’s important that the hot air flows out into your home. If the heat gets trapped inside the furnace, this can lead to overheating and cause damage to various critical parts. Although this problem can get in the way of your family’s comfort, it’s also important to recognize that a blower motor issue can lead to further repairs or a replacement if not handled promptly.

What to Do: Inspect your vents for proper airflow. If you notice a weak airflow — or none at all — this could mean that your blower motor is faulty. When you contact a professional HVAC technician for assistance, they’ll let you know if the blower motor needs to be replaced or if it can be repaired. Our heating experts specialize in everything from furnace replacements to boiler repair in CT, so you can trust us to provide you with a reliable solution.

Blocked Exhaust Flue

Have you checked all the possibilities above but still find yourself asking, “Why is my furnace short-cycling?” There’s one more crucial option worth considering: the exhaust flue is blocked.

Your furnace’s exhaust flue is responsible for venting the noxious gases that are created during the combustion process. This small but mighty component is incredibly important, as it helps prevent these gases from entering your home.

However, it’s important to know that this part isn’t immune to problems. There’s a chance that the flue can become clogged with debris, foreign objects, or an animal’s nest. If the flue detects a blockage, the component will tell the furnace to shut down completely.

What to Do: You can shut off the furnace and disconnect the flue to inspect it for a clog. From here, you might be able to extract the blockage yourself. If you suspect that an animal is in the flue or you don’t feel comfortable handling the job yourself, you should contact a professional for assistance.

Furnace Repair and Maintenance Services in New Haven, CT

Why is my furnace short-cycling? As you can see above, this question isn’t as easy as you might think. There are many possibilities; for example, your furnace could be too large for your home, or you could be experiencing a clogged flue. It might take some troubleshooting before you get to the root cause of the issue.

If you’ve checked your furnace for the problems above and are still dealing with short-cycling problems, don’t wait to contact a professional HVAC company for help.

If your furnace is experiencing unexplained short cycling, it means its efficiency is rapidly declining. The cumulative cost of repair may surpass a new unit’s price, and you should consider replacements over continuous maintenance. When you need a gas furnace service in CT because of a short-cycling heater, turn to your local heating and air conditioning company for assistance. We offer everything from heating system repairs to air conditioning replacement in New Haven to keep your home comfortable!
If you need help with your HVAC system, contact Air Specialties. We are a local company offering furnace repair and furnace maintenance in New Haven, CT. Get in touch with us today for more information about what we can do for you!

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