Is Your Furnace Cycling Too Often? Here’s What’s Wrong

As the weather gets colder, your family is going to rely heavily on your home’s furnace to keep them warm and comfortable. You simply can’t do without it. Keep in mind, however, that it’s been sitting for a few months when the weather was warm. During that time, it may have developed a problem that affects its ability to work properly and require furnace repair service. One of the most common problems is called short cycling which makes it difficult for the furnace to produce adequate heat, uses excessive energy, and may even damage the unit.

What Is Short Cycling?

Furnaces work on a cycle that produces heat to bring the air up to the desired temperature, shuts down, and heats again at regular intervals. Short cycling is when the furnace comes on for a short time and then goes off again without heating the air completely. If your furnace seems to be running constantly, or going off and on at seemingly random intervals, you’ll also notice a spike in your utility bills when you use it. If the problem isn’t resolved, it can cause damage to your furnace resulting in costly repairs or a replacement heating system.

What Causes Short Cycling?

The only way to know for sure what’s causing your furnace to short cycle is to have it inspected by an HVAC company. However, there are 5 main reasons that your furnace might be short cycling. While most of these causes are not something a homeowner can fix, it’s good to know what you might be up against.

  1. Dirty Air Filters – The number one reason for short cycling is a dirty furnace air filter. When the filter is dirty, it restricts the flow of air to the heat exchanger which causes the furnace to overheat and shut down quickly. Thankfully, this is an easy fix. Just replace the old filter and make sure to change it every 30 to 60 days depending on how dirty it gets.
  2. Blocked Vents – Airflow is an essential component of a furnace. If an exhaust vent or interior vent is blocked, it will restrict the flow, much like a dirty air filter and cause the furnace to malfunction. Check your interior return air vents and make sure they’re not blocked off by furniture or other obstructions. If your exhaust vent seems to be the problem, call someone in to take a look.
  3. Misplaced Thermostat – Another common cause of short cycling is a thermostat that’s located close to a heat source like a vent. Whenever hot air comes in contact with the thermostat, it shuts the furnace down, only to fire it up again when the airflow stops. Your thermostat should be located in a place that best reflects the average temperature of your home. An HVAC professional can help you with this.
  4. Dirty or Corroded Sensors – The flame sensor in your furnace is in place to ensure the gas gets shut off if the flame is not lit. Its purpose is to keep gas from building up in your home. If the sensor is dirty or corroded, it won’t be able to sense the flame and will shut the gas off to the furnace. If you suspect a sensor problem, ask a professional to take a look and make the necessary repairs.
  5. Your Furnace Is Too Big – Bigger isn’t always better, especially when it comes to your home’s furnace. If it’s too big, it’ll heat your home quickly, but cycle off and on frequently to keep it up to temperature. It’s highly inefficient and wastes tons of energy. The only solution to this problem is to replace it with a unit that is appropriately sized and that means consulting an HVAC expert for advice.



If your furnace is exhibiting signs of short cycling, don’t let it go on for too long. Those short cycles create a lot of wear and tear on your furnace and can cause serious damage to its components. If left unchecked, short cycling will eventually cause your furnace to stop working altogether, leaving you and your family in the cold. Contact us to learn more about furnace short cycling, or to schedule a heating system tune-up, repair, or replacement.