What Is Considered A Furnace Short Cycling?

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What Is Considered A Furnace Short Cycling?

What is Considered a Furnace Short Cycling?

Many times, Kotz Heating, Cooling, and Plumbing has to tell our customers in Waterford, MI and Oxford, MI their furnace needs repairs because it is “short cycling.” Often the immediate response is something like what sort of mambo-jumbo is that? I assure you the problem is very real and requires immediate attention.


When a furnace shuts down before reaching the desired temperature it’s a “short cycle.” This means that if your thermostat is set at 70 degrees, the furnace shuts down at say 66 or 68 degrees. Short cycling also describes a situation where a furnace turns on and off repeatedly. A typical heating cycle should last several minutes. The frequency depends mostly on how cold it is outside. If it cycles too frequently and only runs for a minute or two there is a problem and it’s causing undue wear and tear on your expensive heating system.


In some cases, your furnace is shutting down to protect you and your family from potentially dangerous situations. Modern furnaces have built-in safety systems to prevent fires, carbon monoxide poisoning, and gas leaks. Let’s take a closer look at some of the leading causes of short cycling:

  1. A clogged air filter – This means the blower fan isn’t able to move enough air over the heat exchanger. If the heat exchanger overheats it will trip the fan limiter and shut the system down.
  2. A clogged flue – This can happen if something falls into the vent pipe, or a bird or other critter has constructed a nest. When it happens the flue limiter shuts down the furnace to protect you from carbon monoxide poisoning.
  3. A malfunctioning thermostat – This can also cause the furnace to cycle too frequently and keep it from reaching the desired temperature. Sometimes it can be fixed by simply changing batteries if your thermostat has them.
  4. A dirty flame sensor – This is what senses the presence of flames and allows gas to flow. When the flame sensor is dirty or damaged it shuts off the gas valve to prevent natural gas accumulations that could cause a fire. This is easily prevented with regular furnace maintenance.
  5. A damaged igniter – When the igniter (pilot light in older furnaces) fails to work the furnace will shut down to prevent a fire or explosion caused by gas accumulations.
  6. An oversized furnaceToo many HVAC contractors are guilty of thinking bigger is better and that’s just not true when it comes to furnaces. When the heating system is too large it may cycle on and off repeatedly. While not inherently dangerous, it’s not a good thing. It means larger utility bills, increased furnace maintenance, and shorter equipment life. Unfortunately, the only solution is a system replacement.


Ultimately, short cycling means your Waterford, MI or Oxford, MI home may not be comfortable and that’s not acceptable. Call Kotz Heating, Cooling, and Plumbing for any furnace maintenance needs. Be sure to like us on Facebook and follow us on Twitter to learn more about the services we offer.