ac repair Pelham, Al

What to Do If Your Furnace is Short-Cycling

That was fast. Cooler weather showed up very quickly on our doorsteps and you probably turned on the heat for the first time. Because winter is quickly approaching, you want to ensure your furnace is working properly at keeping your home warm and your family comfortable. A common issue that you may experience with your furnace is that it is short-cycling or overheating. What is short cycling and how will you know? Short cycling means that the furnace turns on and off very frequently with little time between on and off. If you feel like hardly any heat came from your registers before the unit shut off again, it may be short cycling. If this becomes a pattern of on and off and on and off, go ahead and give Autumn Air Home Services a call so we can diagnose the problem and find a solution that makes your home comfortable again. 

Why Does a Furnace Short Cycle? What causes it?   

Some common reasons include:

  • Overheating
  • Bad flame sensor 
  • Dirty furnace
  • Blocked heat grates/ registers
  • Blocked exhaust vent
  • Thermostat is in the wrong location
  • Furnace is too big for your home


Sometimes a furnace will short cycle to protect itself from damage. It may turn off prematurely if it’s overheating. An overheating furnace can potentially create cracks in the heat exchanger, which can be very harmful for your family if carbon monoxide leaks into your home. So if that’s why your unit is short cycling, then what is causing it to overheat? Do you have to have the whole furnace replaced? Not necessarily. There are many reasons a furnace may get overheated and cause short cycling: 

  • Your Furnace Filter is Dirty

A dirty filter can cause overheating. A sign is that you feel hotter than usual air coming out of the registers. If the furnace gets too hot, the switch will shut down the furnace for safety. A dirty filter in your returns prevents a flow of return air into the furnace, and without that air, it will quickly overheat and turn off. The solution is super simple- change your filters out regularly (several times a year). 

  • You Have a Bad Flame Sensor 

A bad flame sensor means that the furnace flame will shut off almost immediately after lighting. In order to determine whether this is the cause, remove the cover from the furnace to look for the burner firing. The motor will run approximately 30-60 seconds before the gas fires, if you find that it isn’t firing then this may be the issue. 

The flame sensors help make sure raw gas isn’t being pumped into your home. If the sensor doesn’t sense a flame, it will shut off the gas valve. The solution is to clean or replace the flame sensor which can be done by one of our Autumn Air technicians. 

  • Your Registers Are Blocked

This is another common reason your furnace might overheat- it doesn’t let enough air out of the system. The registers in your floor, walls, or ceiling likely have a way to close them, allowing you to control which rooms get heat. If too many of these vents are closed your furnace can’t disperse enough heat, so the heat will build up in the furnace, causing it to overheat and shut down. Make sure that at least 75% of your registers are open and not being blocked by furniture or anything else. 

  • The Exhaust Vent is Blocked

This is another cause of overheating and short cycling but can be more dangerous since it can allow carbon monoxide through the vent.  Typically, the exhaust vent becomes blocked by birds’ nests from birds, beehives, or something else. If you check it out and realize the cause is a nest, it may be best to have animal control or pest control handle the task.

Thermostat Issues

Short cycling could be as simple as a thermostat placement issue. The location of your thermostat matters because if your thermostat is getting warmed before the rest of the house, it will cause your furnace to turn off prematurely.

Poor placement for your thermostat includes right above a register or on the wall of the utility closet where the furnace is located. If placed here, the thermostat will heat quickly and reach its set point before it should. The solution is easy! Just relocate the thermostat to a location that isn’t near a vent or window.

If you believe your furnace is short cycling or overheating, contact Autumn Air for full HVAC services in Pelham, AL and surrounding communities. It might be something as simple as a thermostat issue, or something more serious, so it’s always best to have professionals take a look and make the necessary adjustments.

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Birmingham, AL 35244

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