Tuckers Air Conditioning, Heating & Plumbing Blog

Why Does My Furnace Start and Stop So Much?


If you’ve used the same furnace for at least a few years, you’ll have an idea how long it stays on each time it fires up to start a heating cycle. You may not pay special attention to it, but you’ll have a subconscious concept of how long it usually runs during a typical winter day. 

When the furnace begins to turn on and off more often, you’re likely to notice it. And since you’re here reading this, you have some idea that this shouldn’t be happening. It’s abnormal and may mean something is wrong that will require you to call us for heating repair in Gaithersburg, MD.


You are probably right that your furnace has a problem. What’s occurring is called short-cycling, and it’s a common symptom of various different malfunctions in a heating system. It often happens with air conditioners, but furnaces can also experience it. 

The problem with short-cycling is that the furnace is failing to complete a full heating cycle. When the furnace turns on (lights the burners, activates the blower fan, sends power to the electrical heating elements) it should remain running for at least 15 minutes before it cycles down. On colder days it will stay on longer until it can reach the setting on the thermostat. If it shuts down early, it will then turn back on again a short time later, then shut down again, and repeat. 

Short-cycling is bad for the furnace. It puts extra strain on its components and drains large amounts of energy because the furnace draws on the most power to start up. But the cause of the short-cycling is often the bigger problem.

Sources of Short-Cycling

The causes of short-cycling in a furnace range from simple issues you can correct on your own to large problems that require replacing the furnace. Here are the more common causes:

  • Clogged air filter: Always change the furnace’s filter every 1–3 months. Otherwise, it can cause the furnace to overheat and shut off early.
  • Faulty thermostat: The thermostat may be sensing incorrect temperatures or is sending incorrect signals to the furnace to stop early. 
  • Blocked room vents: If room vents are obstructed, the rise in pressure inside the ventilation system will cause the furnace’s blower fan to prematurely power down. 
  • Oversized furnace: If your furnace is new, then the trouble might be that it was badly installed so it’s too powerful for your house. It will raise the temperature too fast and shut off early. The only solution to this problem is to have a new furnace installed—and have skilled professionals do it.
  • Aging furnace: For a furnace that’s more than 15 or 20 years old, short-cycling often indicates the system has worn down to the point it can no longer function as normal.

If you can’t tell why your furnace is behaving this way, let our experts find out. We’ll diagnose the issue and have it fixed.

At Tuckers Air Conditioning, Heating & Plumbing, we pledge to exceed expectations at every turn. Reach out to us for heating repair in Washington D.C., Montgomery and Frederick Counties.