5 Reasons Why Your Furnace Cycles On and Off

Facade of newly constructed home.

The heat is on but your furnace won’t turn off—why?

When your home’s furnace turns on and off repeatedly, regardless of the temperature, we call this short cycling. Whether it’s a faulty thermostat, a corroded flame sensor, or some other issue, short cycling is a serious problem that needs to be addressed immediately.

Not only will it result in higher utility bills, but short cycling could cause permanent damage to your furnace.

At AiRCO, we’re proud to serve local families and businesses in the Austin area. Here are a few troubleshooting tips to consider if you suspect your furnace is short cycling. If the problem continues, let us send one of our experienced heating, ventilation, and air conditioning (HVAC) professionals to your home to diagnose the issue and find the right solution for you.


The national average price in 2019 to repair a furnace ranged from $150 to $400, according to Thumbtack.com. Replacing your furnace will likely cost thousands of dollars, not to mention the inconvenience. To avoid unnecessary energy bills, it is vital to maintain your furnace regularly and schedule a tune-up at least once a year.

Air Filters

A clogged air filter, believe it or not, is one of the most common causes for short cycling. Warm air cannot pass through the blocked filter, prompting your thermostat to switch on the furnace repeatedly to heat your house. On average, it’s a good idea to change a 1- to 2-inch air filter every three to four months.

Changing your furnace air filter on a routine basis is relatively inexpensive and a great way to prevent larger problems from occurring.

Blocked Vents

If enough vents are blocked off or closed in your Texas house, it will create a shortage of heat throughout your house and cause your furnace to short cycle. Give your air ducts a break and be sure to keep all your vents open and unobstructed—even in unused rooms.

Check Your Thermostat

Is it time to upgrade your old thermostat? When was the last time you replaced the batteries or checked the wiring? A malfunctioning thermostat may cause your system to short cycle because it’s sending the wrong signal to your furnace.

And when it comes to thermostats, location matters: if your thermostat is located near a heat source, it could make your furnace turn on and off. If that’s the case, call one of our professionals and have it moved to a better spot in your home.

Flame Sensor

When a flame sensor malfunctions, your system cannot detect a flame. This causes your furnace to shut down automatically to prevent gas from getting into your house.

Check to see if the sensor’s porcelain insulation is visibly dirty or corroded—in which case you can clean away the corrosion using fine grit emery cloth. If the insulation is cracked or pieces are missing, you will need to replace the flame sensor.

The Wrong Size

For the most part, the size of a furnace is based on your home’s square footage and climate zone. An oversized furnace will heat up too quickly and then abruptly turn off, leaving parts of the house too hot and other parts too cold. A furnace that is too small will continually run and do a poor job of heating every part of the house.

If your furnace is the wrong size for your home, you will need to replace it. Otherwise, you’re faced with the possibility of high energy bills and constant repairs. If you suspect this is the case, call our experts and have them measure how much heat your house requires based on the square footage.

Give Us a Call Today

If your furnace short cycles, you’re spending more than you need to on energy bills—and you risk the possibility of a permanent malfunction. Call AiRCO at 512.537.1234 or request service online to schedule a routine checkup of your HVAC system here in Austin, TX, and to be sure your furnace is cycling properly.

Need HVAC Service?

Contact the experts at AiRCO Mechanical.

Call us at 512-537-1234!

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