Warning: Undefined array key "options" in /home/hinzanet/ims.hinzanet.com/wp-content/plugins/elementor-pro/modules/theme-builder/widgets/site-logo.php on line 192
Is Your Furnace Short Cycling? Here's What That Means | IMS Heating & Air, Inc. Is Your Furnace Short Cycling? Here's What That Means | IMS Heating & Air, Inc.

Is Your Furnace Short Cycling? Here's What That Means

A normal functioning furnace shuts off when it reaches the temperature set on the thermostat. For instance, if the reading on the thermostat is 72 degrees, it will go off once it achieves that temperature. It will turn on again when the temperatures go below that point.

By doing so, it maintains the desired indoor temperatures and ensures that the furnace doesn’t stay on unnecessarily – this helps save on electricity bills. A normal furnace cycle takes anywhere from 10 to 15 minutes.

However, there are times when the furnace shuts off before reaching the optimum temperatures. Other times, it shuts off and turns on too frequently, not maintaining the normal cycle. This is what is referred to as a furnace short cycling problem. And, in most cases, they last for 3 to 7 minutes.

Usually, furnace short cycling can be a disaster for the homeowner, as the furnace doesn’t heat the house as required. Also, there could be another underlying issue with the furnace that might lead to costly repairs or even replacements.

So, if your furnace keeps short cycling, be sure to continue reading.

The Main Furnace Short Cycling Causes

There are numerous reasons why furnace short cycling occurs. Some of the main causes of furnaces short cycling are:

  • A bad flame sensor
  • Blocked heat grates
  • Thermostat problems 
  • Blocked exhaust vent
  • Dirty furnace filter
  • Incorrect unit size

Let’s explore each of these problems more:

1. A bad flame sensor

A furnace flame sensor is a small metal rod that notifies the furnace of the presence of a flame when the gas valve is open. If the sensor can’t detect a flame, it makes the furnace go off. This is to protect against the gas buildup in the furnace or the house, which can be quite dangerous.

Generally, there are instances when the flame sensor isn’t functioning well. This might be due to clogs caused by dirt and rust or when the sensor has been compromised. In such instances, the flame sensor cannot detect the flame even when it’s present.

As a result, the sensor will instruct the furnace to shut off every time it tries to detect the flame but cannot. A bad flame sensor is, therefore, a major cause of gas furnace short cycling. 

To fix this, the sensor should be cleaned thoroughly to ensure it can detect the flame. And if it’s faulty, it should be replaced.

The best way to handle this is to contact an HVAC professional to inspect your flame sensor properly since it includes working with electricity and dangerous flammable gasses. They will know whether to clean or replace the flame sensor.

2. Thermostat problems

Thermostats tell the furnace what to do – whether to go on or off, based on the room’s temperature levels. If the temperature on the thermostat is 72 degrees, anything above this makes the furnace shut off. On the other hand, when temperatures fall below this, the furnace turns on.

A malfunctioning thermostat might be the next culprit for furnace short cycling issues. And whether it’s a battery issue, incorrect thermostat setting, or faulty thermostat, it might affect the comfort of your home.

Therefore, start by checking the settings on the thermostat. If it’s set too high, this might be the cause of the short cycling problems, and you need to scale it down. If this isn’t the issue, check the batteries and replace them if they are dead or weak.

However, if the furnace is faulty, you might need to call a professional for a proper assessment. They will check the thermostat to determine the cause of the problem and offer a solution.

3. Blocked heat grates

The third possible cause of a furnace short cycling problem is blockage of the heat grates.  Blocked heat grates do not let enough hot air out of your unit. As such, the trapped hot air causes the furnace to overheat and eventually short cycle.

In this scenario, you will notice that your furnace has stopped operating 3 to 10 minutes before your house is warm. To fix this, ensure that nothing is blocking the heat grates and that the warm air is flowing well from the heating unit to the house.

4. Blocked exhaust vent

A blocked exhaust vent is dangerous since it restricts the proper expelling of carbon monoxide outdoors. And if this finds a way to your house, it can cause serious health issues.

A blocked exhaust vent also means that airflow is restricted, which can easily cause overheating. When the unit overheats, the result will undoubtedly be short cycling.

For this reason, ensure that nothing is blocking the end of your unit’s exhaust vent. Remove any beehives, rodents and birds’ nests, snow, or any other obstructions.

5. Incorrect furnace size

Sometimes we think that large furnaces are ideal for heating our homes. However, this isn’t the case, especially if the furnace is too large.

An oversized furnace will heat the house fast but unevenly. This means that some rooms will be warmer than others, which in most cases, confuses the thermostat. As a result, the furnace will keep short cycling as it tries to achieve uniform heating.

The solution here is to get an appropriately-sized furnace for your home. This ensures that the house is evenly heated and avoids unnecessary high energy bills. Reach out to an HVAC company, like our award-winning team at IMS Heating & Air, when buying or installing a new furnace to help you get the right unit for your home.

6. Dirty or clogged furnace filter

A dirty filter can result in insufficient airflow in the unit. As a result, the warmed air can get trapped inside the unit, and there is no sufficient return air. This causes the temperatures in the furnace to rise, which leads to overheating, and subsequent shutting off.

Also, if all the heated air isn’t dispelled into the rooms, it means that the indoor temperatures are always below the thermostat’s settings. Consequently, the thermostat will trigger the furnace to start, an action that leads to short cycling of the furnace.

Luckily, keeping your unit clean will sort out this problem. Plus, you can even clean or change the air filters by yourself without involving a technician. 


If you need a qualified technician to do the job, contact IMS Heating & Air. Our talented team has the skills and know-how to get your heating system up and running, regardless of how big or small the issue may be.