Blog

Bad Thermostat: If your thermostat has a problem, it can cause your furnace to run cycles that are either too long or too short. If the thermostat is sensing the incorrect temperature and not sending a cut-off signal soon enough, or if the battery is dying, your thermostat can cause your furnace to run erratically.

Low airflow

When the exchanger heats up to the maximum temperature, the furnace shuts off after a few minutes. ... The furnace won't be able to pull fresh air into the blower if the air filters are clogged with dust, pet hair, and other debris. You should also make sure to open all of your air supply vents.Oct 3, 2019

First, check for your gas burners to light up and then go out after a few seconds. This is the most common sign of a sensor issue. Second, if you can actual see soot covering the tip of the sensor, it's time for a cleaning. If you look at the tip and it's black, it's time for service.Jan 22, 2019

A furnace that is short cycling turns on and then turns off before it has heated your home to the thermostat set point. Sometimes a short cycling furnace won’t make any heat at all before shutting down. Why does a furnace short cycle?

Your blower should run constantly until the heating cycle ends. When your furnace isn’t actually heating, though, your furnace blower shouldn’t be running at all.

Blocked Exhaust Vent This is another cause of a furnace overheating and short cycling. Short cycle time: 1-5 minutes. This issue can be dangerous too, since deadly carbon monoxide is dispersed through the vent. If it is blocked, the gas won’t escape, and it can leak out of the furnace and into your home.

Short cycle time: 3-7 minutes in most cases. When a furnace is the right size for a house, the heating cycles are long. They don’t produce noticeable temperature swings.

Your thermostat could also cause the HVAC system to cycle on and off rapidly, a process known as short cycling. Your furnace or central air conditioner spends a good amount of energy simply turning on and off, which is why you want yours to run for at least 15 minutes at a time before shutting off.Oct 2, 2017

Frozen evaporator coils are a common cause of short cycling. Sometimes, air conditioners freeze up when they're running while it's too cold outside, usually at night. In other cases, freezing may be caused by a dirty filter or a mechanical problem. Shut your system down, allow it to thaw completely, then run it again.Apr 27, 2019

With all that being said, if there are no extreme factors involved, the average run time for a furnace is 10-15 minutes per cycle. Your furnace may need to run two to three times an hour to maintain your desired temperature if your home has average insulation.

The most likely cause of short cycling is the fan limiter, which prevents fires and furnace damage by shutting the system down if the heat exchanger becomes too hot. ... A dirty flame sensor or damaged thermocouple will shut off the gas valve and the furnace. This prevents natural gas accumulations that could cause a fire.

Closed or Blocked Air Supply Vents.

If your furnace keeps shutting off, check your air vents to see if any of them are closed or blocked in any way. You should keep all your vents open, even in the rooms you don't use. ... Then that heat builds up and could end up causing your furnace to short cycle.

A dirty filter can cause the furnace to overheat. Short cycle time: 2-5 minutes. ... If the furnace gets too hot, the switch shuts down the furnace. A dirty filter prevents a flow of fresh, cool air into the furnace to be heated and dispersed.

Your furnace should kick on and stay on until it reaches the temperature set on your thermostat. Short cycling occurs when your furnace turns on between four and seven seconds and then shuts off without heating your home.Nov 20, 2020

A faulty thermostat can be a possible culprit for short cycling. If you're experiencing a furnace short cycling, the first and easy thing you can do is check your thermostat to see if it's performing correctly. Many times, a homeowner may forget to switch their thermostat over to the heating mode.Sep 2, 2021

If the run-time sounds shorter than normal, the heater may have a problem called short-cycling. Short-cycling is when a heater doesn't complete its regular heating cycle and turns off early. ... If your heater keeps turning off after only five minutes, that's too short—no matter how low you've set the thermostat.Mar 24, 2020

Low airflow

When the exchanger heats up to the maximum temperature, the furnace shuts off after a few minutes. ... The furnace won't be able to pull fresh air into the blower if the air filters are clogged with dust, pet hair, and other debris. You should also make sure to open all of your air supply vents.Oct 3, 2019

• The Danger of Furnace Short Cycling. As you use your furnace to stay warm this winter, you need to keep an eye out for any problems that can occur due to the increased stress on the system. One of the most dangerous problems a furnace can be afflicted with is short cycling.

• Furnaces should cycle at least three to six times per hour. Depending on the furnace model, it may also run five minutes on, then five minutes off.

Short cycle time: 3-7 minutes in most cases. When a furnace is the right size for a house, the heating cycles are long. They don’t produce noticeable temperature swings. When a furnace is too big, it can short cycle – start, heat up air very quickly that reaches the thermostat, and then shut down.

The most likely cause of short cycling is the fan limiter, which prevents fires and furnace damage by shutting the system down if the heat exchanger becomes too hot. ... A dirty flame sensor or damaged thermocouple will shut off the gas valve and the furnace. This prevents natural gas accumulations that could cause a fire.

First, check for your gas burners to light up and then go out after a few seconds. This is the most common sign of a sensor issue. Second, if you can actual see soot covering the tip of the sensor, it's time for a cleaning. If you look at the tip and it's black, it's time for service.Jan 22, 2019

A faulty heat exchanger can also cause short cycling. In worst-case scenarios, a cracked heat exchanger will emit heat into other components of your furnace. As a result, your furnace may overheat and experience short cycling.

The easiest way to fix a furnace that is short cycling is to remove the flame sensor to clean it. Use a sponge or brush to remove the dirt from the sensor. After the part is clean, follow the manufacturer's instructions to insert the flame sensor into the furnace.Nov 10, 2020

A common reason a furnace short cycles is because the heat exchanger, the part that heats your air, is getting too hot due to a lack of airflow. Once the heat exchanger overheats, it trips the high limit switch, which shuts the furnace down to protect it.Dec 9, 2016

Your thermostat could also cause the HVAC system to cycle on and off rapidly, a process known as short cycling. Your furnace or central air conditioner spends a good amount of energy simply turning on and off, which is why you want yours to run for at least 15 minutes at a time before shutting off.Oct 2, 2017

Short cycling is when the furnace turns on for a short period of time but then turns off. This start-and-stop cycle can keep your home from properly warming up and may also damage your furnace itself.Oct 24, 2017

Short cycling doesn't necessarily pose a threat to your health, but it can absolutely destroy the furnace if it isn't properly addressed in time.Feb 19, 2018

A dirty filter doesn't let enough air in. This problem doesn't let enough air out of the system. Short cycle time: 3-10 minutes. Again, the furnace will stop before your home is warm.

So, if your furnace keeps turning off and on too quickly, your thermostat might be malfunctioning or broken. There are several things that could be causing your thermostat to not work properly. The wiring could be old and need replacing, it might need new batteries, or it could be the location of your thermostat.

One of the most common, and unfortunately harmful, problems an air conditioner can have is something called short-cycling. This is both a symptom of a problem and a cause of a problem. Sometimes a few simple adjustments may be all that's needed to repair the issue.Jul 8, 2019

The biggest problem with short-cycling is that it increases wear and tear on your air conditioner. Sure, short-cycling is a warning of a problem–like a refrigerant leak. ... Your air conditioner's compressor accumulates extensive wear and tear which can cause the system to overheat and burn-out as a result.Jul 20, 2020

If that capacitor is failing, your system may not sustain enough current to stay up and running. That is why short cycling is such a common sign of a failing capacitor. ... If your thermostat is not reading temperatures accurately, then it may lead to short cycling.Apr 11, 2016

During hot weather, your heat pump's refrigerant absorbs heat from inside your home and sends it outside. During cold weather, the process is reversed. If you have a refrigerant leak, your system is going to have trouble with the heat transfer. Consequently, it will come up short in trying to complete a cycle.Sep 14, 2020

• If your furnace is short cycling on a continual basis, the fix may be as simple as replacing your current thermostat with a new one. You can either buy one yourself at the store, or have a professional install one for you. Also be sure to check the location of your thermostat in your home.

• Reasons for Furnace Short Cycling A Bad Flame Sensor (aka Flame Rod) The furnace flame will shut off almost immediately after it lights. Short cycle time: A few seconds after the burner fires. ... A Very Dirty Furnace Filter A dirty filter can cause the furnace to overheat. Short cycle time: 2-5 minutes. ... Closed Heat Grates This is another cause of overheating inside the furnace. ... More items...

• Sometimes short-cycling occurs due to a system fault, and it sometimes occurs due to a mismatch between system capacity and load (cooling or heating too quickly). Short-cycling is a problem for many reasons, including poor temperature control, inadequate dehumidification, rapid component failure, and the list goes on and on.

• This on-off cycling keeps your Yardley home from heating up properly. This action – called short cycling – also requires more electricity and drives up utility bills. Short cycling is caused by an overheated furnace, which triggers safety mechanisms and shuts down the furnace.

If your furnace is short cycling on a continual basis, the fix may be as simple as replacing your current thermostat with a new one. You can either buy one yourself at the store, or have a professional install one for you. Also be sure to check the location of your thermostat in your home.

Reasons for Furnace Short Cycling A Bad Flame Sensor (aka Flame Rod) The furnace flame will shut off almost immediately after it lights. Short cycle time: A few seconds after the burner fires. ... A Very Dirty Furnace Filter A dirty filter can cause the furnace to overheat. Short cycle time: 2-5 minutes. ... Closed Heat Grates This is another cause of overheating inside the furnace. ... More items...

Sometimes short-cycling occurs due to a system fault, and it sometimes occurs due to a mismatch between system capacity and load (cooling or heating too quickly). Short-cycling is a problem for many reasons, including poor temperature control, inadequate dehumidification, rapid component failure, and the list goes on and on.

This on-off cycling keeps your Yardley home from heating up properly. This action – called short cycling – also requires more electricity and drives up utility bills. Short cycling is caused by an overheated furnace, which triggers safety mechanisms and shuts down the furnace.

The most common issues that can cause your furnace to stop and start again are: ... Restricted Airflow: Your furnace draws in air from your home and then cycles the warm air back into your home. If your intake vents and exhaust vents are blocked or airflow is restricted, then you could experience short cycling.Sep 17, 2020

Your thermostat is what controls your entire heating system. So, if your furnace keeps turning off and on too quickly, your thermostat might be malfunctioning or broken. ... The wiring could be old and need replacing, it might need new batteries, or it could be the location of your thermostat.

If you have a faulty blower motor, you may experience low airflow from the vents, even when the fan is on high. There will be no air coming from the vents if your fan isn't working due to a bad blower motor resistor.

On average, furnaces should kick on and turn off anywhere from three to eight times per hour. However, if your furnace turns on and off more frequently, don't assume the furnace is short cycling just yet.Dec 8, 2020

Incorrect Unit Size: An HVAC unit that is too large or too small for the space it's in can lead to short cycling. ... An Overheated HVAC Unit: If airflow is restricted due to dirty air filters, blockages in air ducts or bent fins on air vents, heated air will remain trapped, eventually overheating your system.Nov 25, 2020

For most heating application, the thermostat detects the temperature in a given spot in the house. When it is colder than 74℉, it switches a relay indicating to the furnace to start heating.

• If your furnace is short cycling, it could also be any one of the following issues: The blower motor is what circulates the air throughout your house. It's possible your furnace will run when the blower motor is off; however, that's rare.

• Thanks to reader Tim (2019/04/12) we have first to distinguish three different furnace burner or blower-fan on-off cycling problems: CASE 1: furnace BURNER cycles ON-OFF during a call for heat, BLOWER remains ON - high limit rocking CASE 2: furnace BLOWER FAN cycles ON-OFF while BURNER remains ON - blower short-cycling

• For a furnace with adequate duct work this heat rise should fall in the range of 45 degrees to 70 degrees. Anything that causes overheating in the warm air supply plenum will cause furnace short cycling. Common causes of heating furnace short cycling or rocking are listed here alphabetically.

• Short cycle time: A few seconds after the burner fires. Don’t mistake the draft inducer motor starting for the furnace burner firing. The inducer motor starts 30-60 seconds before the gas fires.

Clogged Exhaust Vent. If your furnace is turning on for only 1-5 minutes at a time, chances are it's a clogged exhaust vent. This can pose a potential threat to the safety of your home: with a blocked vent, carbon monoxide has nowhere to go and can leak out of the furnace and into your home.Dec 16, 2020

Still, you can generally expect your thermostat to last at least 10 years. After a decade, thermostats may start malfunctioning. The thermostat's wiring starts to age, dust accumulates within the system, and the parts begin to wear down.Nov 23, 2021

In this case the blower will remain off but the fan turns on and off one or more times after the thermostat has stopped calling for heat. Blower fan short cycling on and off too frequently during the heating cycle is often traced to this problem. Why would we have "abnormally low incoming air temperature" at a furnace?

If your furnace fan is set to AUTO and is still running, then move on to the next section. Your fan limit switch is located directly under your furnace hood and controls when your furnace blower turns on and off.

In normal operation, your furnace blower fan should come on 1.5 to 3 minutes after your thermostat calls for heat and should turn off several minutes after the heating cycle ends. Your blower should run constantly until the heating cycle ends. When your furnace isn’t actually heating, though, your furnace blower shouldn’t be running at all.

FAN-OFF: the lowest temperature setting (blue arrow, the left end of the dial) is the "FAN OFF" temperature. The FAN OFF setting lets the furnace blower continue to run for an interval after the furnace burner has turned off, but will shut the blower off after the heat exchanger has been cooled down to this temperature (usually 90 °F).

A furnace that is short cycling turns on and then turns off before it has heated your home to the thermostat set point. Sometimes a short cycling furnace won’t make any heat at all before shutting down. Why does a furnace short cycle? Solutions for each of these problems are found below. Most causes are easy to fix.

Bad Flame Sensor

Flame sensors are also subject to corrosion. This is because your furnace produces small amounts of water during the heating cycle. Over time, this can lead to corrosion and rust in your furnace, resulting in short cycling.Oct 14, 2021

When a furnace starts and shuts off, it could be a sign that you have low airflow. The heat exchanger in the furnace will often overheat if there isn't enough airflow. ... When the exchanger heats up to the maximum temperature, the furnace shuts off after a few minutes.Oct 3, 2019

If your furnace won't turn off, the easiest issue to fix is your thermostat. ... This keeps your fan running constantly, even if the furnace isn't producing hot air. If your blower is still running even after the temperature and fan switch have been adjusted, it's time to go to your furnace and check out the air filter.

• Electric furnaces typically cost more than gas furnaces. A gas furnace will always be more affordable than an electric one. There are other considerations above and beyond just the cost. Electric furnaces do not produce flames and consequently do not generate carbon emissions.