Why Does My Gas Furnace Cycle On and Off Frequently?

If your gas furnace frequently turns on and off, it’s probably “short-cycling," which happens when your furnace is overworking to heat your home, and several factors can cause it.

To help you understand what’s going on behind the scenes of your furnace, we’ll look into what short-cycling is as well as the common reasons why short-cycling occurs:

We’ll also explore how to fix each problem so you can avoid expensive repairs and have your heating comfort restored.

Under normal conditions, once you’ve set your thermostat to your desired temperature, your furnace will kick on to heat your home. After it’s finished blowing warm air, it will turn off for a set period of time before coming back on for another cycle of heating.

Unfortunately, if there’s a problem behind the scenes (which we’ll go into below), your furnace will “short-cycle." It will shut off before completing a normal heating cycle and turn back on without a healthy rest period.

Short-cycling is not good for your system, regardless of whether you have a gas or electric furnace. It puts stress on your equipment, causes parts to wear out faster, and ultimately runs up your energy bills due to the constant starting and stopping. Worst of all, your comfort decreases with uneven temperatures in your home.

If you hear your furnace turning on and off every few minutes or so, it’s time to call in an HVAC technician for maintenance or a repair diagnostic. For example, MSP’s heating technicians are trained to service any brand or model of gas furnace, no matter its age or condition. And with a century of trusted service in the Twin Cities area, you can count on us to put your mind at ease. Call today: (651) 228-9200. We’re here for you 24/7!

Now let’s look into some causes for why your gas furnace is short-cycling.

When installing a gas furnace, bigger isn’t always better. In fact, if your system is too big for the needs of your home, it will quickly begin to short-cycle.

Here’s why:

When you set your thermostat, your furnace will come on to start heating your air. However, because of its oversized capacity, your furnace will heat your space too fast and then shut off early. Furthermore, when your furnace blows so much warm air, you’ll end up with hot and cold spots in your home. And because your thermostat detects uneven heating, it will trigger your furnace to come back on sooner than necessary.

Not only does this waste fuel (which can be expensive, depending on how much natural gas or propane costs in your area), it also puts an undue strain on your entire HVAC system, limiting its lifespan.

Gas furnaces are much more expensive to replace than electric ones. So to protect your heating investment, it pays to install the correctly sized system for your home.

Before recommending a new gas furnace to customers, MSP’s honest and highly trained technicians will perform a free on-site estimate complete with a load calculation to assess your home’s size, layout, and energy requirements. That way, your furnace runs smoothly and efficiently for years to come.

Dirty air filters are one of the most common reasons a gas furnace will short-cycle.

Even if you have the right-sized system for your home’s size and comfort preferences, if your air filters are clogged with dust, dirt, hair, and other particles, the blocked airflow will quickly create a problem for the furnace’s heat exchanger.

The heat exchanger is a critical component of every gas furnace as it creates heat. It relies on a healthy intake of cool air to function, so if clogged air filters stop the flow of fresh air, the heat exchanger will overheat and then shut off for safety reasons. Then, because your home hasn’t reached its desired temperature level, the thermostat will tell your furnace to turn back on, leading to a constant on-and-off cycle.

If left untreated, your clogged air filter could lead to some pretty severe repairs—either a heat exchanger replacement (which averages $2,000) or even a total system replacement. It’s wise to have your air filters cleaned or replaced regularly to avoid financial headaches and stress.

At MSP, our heating technicians always check air filters during a gas furnace tune-up. If you haven’t had maintenance performed in a while, consider scheduling a service appointment. You’ll enjoy decreased energy bills and keep your manufacturer’s warranty valid.

Just like clogged air filters, blocked air vents can also cause your gas furnace to short-cycle.

When you close or obstruct your vents, pressure builds inside of your air ducts. And with less air circulating, the heat exchanger will go into overdrive, causing your furnace to turn off and on frequently.

Make sure to check your supply and return vents so that nothing is blocking them from receiving or dispersing air. If they’re covered in dust or dirt, give them a good clean so that air can flow easily.

Gas furnaces also have a dedicated exhaust vent, allowing toxic gases like carbon monoxide produced during the combustion process to escape outdoors. If the flue pipe is clogged with leaves or debris, similar issues occur with the heat exchanger overworking and short-cycling.

Another benefit of hiring a professional HVAC technician to perform routine maintenance? They’ll check your exhaust vent to make sure everything is flowing properly.

Whether due to low batteries, faulty wiring, or other electrical malfunctions, your thermostat could be causing your gas furnace to short-cycle.

Since its job is to tell your furnace what to do, your furnace could be taking directions to shut off and then come back on frequently, even if your home has already reached your desired temperature.

Check your thermostat’s display screen to see if you can visibly see anything off with it. If you’re not sure, schedule a qualified HVAC technician to take a look.

At MSP, we provide convenient same-day service and upfront repair quotes. We’ll perform a comprehensive diagnostic to identify the root cause of your short-cycling problem. Whether it’s due to the thermostat, air filters, or more, rest assured that we’ll help you get it fixed in no time!