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Short Cycling Furnace

Furnace Starts & Stops? Why Your Furnace Is Short Cycling

Do you suspect that you have a short cycling furnace on your hands?

Depending upon the cause, this can either be a simple fix that a homeowner comfortable with diagnosing issues can perform, or it may be a more complex issue that a professional HVAC contractor will have to fix.

Need help ASAP? Contact the Modern HVAC team or call (920) 733-4713 today!

What is a Short Cycling Furnace?

First, if you’re unsure of whether your furnace is short-cycling, and what that even means, let’s go over that now.

If your furnace is short cycling, it can refer to one of two things:

1.) Your furnace’s heating cycles are reaching short of the thermostat’s set temperature.

We say that a furnace is short cycling whenever it shuts off before it reaches the desired temperature in your home.

For example, if you have your thermostat set at 70 degrees, your short cycling furnace may only ever reach 65-68 degrees.

2.) Your furnace is running more frequently and for shorter periods.

If you are hearing your furnace start up and shut off more often than normal, like every other minute or so, then there is likely an issue with your unit. This type of furnace problem is also called short cycling.

Often, the latter happens during the winter months when you need the furnace the most. Either way, if your furnace is short cycling, your house is most likely not reaching the desired temperature.

Note: You may not have to worry as most heating and furnace systems don’t run constantly, but rather cycle on and off about 3-8 times an hour. However, if your furnace starts and stops more than that, there may be an underlying issue. If the latter is the case, then read on for more info.

7 Possible Reasons Why Your Furnace Is Short Cycling

Does your furnace seem like it’s running abnormally?

If your furnace short cycles or shuts off constantly, you’ll want to take a look at our seven reasons why your furnace starts and stops so frequently and what you (or a certified technician) can do to diagnose the problem.

Furnace Short Cycling - Clean Air Filter

1. You Have a Clogged Air Filter

One common explanation for a furnace starting and stopping repeatedly/furnace short cycling is that your air filter is clogged with dust and dirt.

When this occurs, the airflow to the heat exchanger becomes restricted, and the component overheats. This, in turn, triggers the high limit switch or also known as the safety shutoff. You’ll want to check for dirty air filters frequently.

Here’s what you can do to resolve your short cycling furnace:

The Fix

  • Turn off the furnace and change the filter. A simple fix to this common problem of a furnace stopping and starting repeatedly is to turn off the furnace altogether and change the filter (if you have a disposable type of filter). Permanent filters, which do a better job of protecting your furnace from short cycling, have the benefit of being more eco-friendly since they are designed to be cleaned and reused.
  • Inspect your filter and clean it every 1-3 months. Depending on the filter you have, you’ll need to clean it or replace it every 30- 90 days. Be sure to check for instructions for your particular furnace model.
  • Improve airflow. For even better airflow, try opening some of your vents and have your furnace blower wheel cleaned.

2. Your Thermostat Is The Problem

Yes, if your furnace starts and stops, it may just be related to your standard, smart, or programmable thermostat. Issues with your thermostat can include not being turned on for some reason, or it’s malfunctioning. Here’s how to troubleshoot your thermostat issue:

The Fix

  • Check your thermostat to determine if it is turned on. Make sure it’s switched to “HEAT” and set at the correct temperature. If the temperature setting is too low, your furnace will shut off more frequently.
  • Consider thermostat location as well. The thermostat should be positioned away from sources of heat or cold and mounted about 5 feet above floor level. Ensure that it isn’t mounted too high because, as you may remember from science class, hot air rises. If the thermostat registers extreme temperatures, a shortened furnace cycle may result.
  • The thermostat itself may be malfunctioning. Is your thermostat not sending a signal to your furnace? Be sure to check this out with a person who lives with you. One person should stand next to the thermostat, and the other next to the furnace. Slowly raise the thermostat setting and listen for noise from the furnace. The lack of any sound indicates that you may need professional thermostat repair or replacement. Learn more here about how to choose the right thermostat for your furnace to ensure thermostat and furnace compatibility.
  • The thermostat needs new batteries. You should check with your HVAC technician or the owner’s manual to see how often your thermostat’s batteries need to be changed. If your thermostat needs to operate on batteries, you should try to change them every 6 months to prevent the chances of a short cycling furnace.

3. The Flue or Vent Pipe is Clogged/Damaged

Another possibility is that the furnace’s flue or vent pipe is either clogged by an object such as a bird or rodent nest. A clogged or damaged flue or vent pipe may cause the heat exchanger to overheat. Left unchecked, this may result in tripping the fan limiter and even shutting the furnace down altogether.

The fan limiter helps to prevent the heat exchanger from overheating and starting a fire or damage (e.g. cracking and causing carbon monoxide leaks).

The Fix

  • Check to see whether clogging in the flue or vent pipe is possible. Try to safely remove if you are comfortable with DIY work. If possible, also check the fan limiter and heat exchanger.
  • Contact a trusted local HVAC technician for assistance with the removal. The benefit of contacting a technician is that they can inform you of any other potential issues also.

4. You Have A Dirty or Malfunctioning Flame Sensor

If your furnace starts and stops repeatedly, you may want to check out its flame sensor.

The gas furnace’s flame sensor is a safety device that cuts off the supply of natural gas when no flame is detected. If your flame sensor develops soot or corrosion, it can’t function properly and will keep turning off the gas valve.

The Fix

  • Schedule a service request. If you suspect that you have the problem of a dirty or even a malfunctioning flame sensor, be sure to get an expert furnace repair as soon as possible.

5. There is a Damaged Igniter

Another possible reason why your furnace is short cycling is thanks to a damaged igniter.

When a hot surface igniter (or a pilot light on older models goes out), the furnace will respond by shutting down to prevent dangerous gas accumulation.

The Fix

  • Have a professional assess your furnace for a damaged igniter. You may need to get it replaced in order to get your furnace back in working order.

6. A Fan Limiter Failure Has Occurred

We mentioned this earlier, but it’s important to also consider the fan limiter as a possible issue.

The fan limiter in your furnace helps to prevent the heat exchanger from becoming too hot where a fire would start or the heat exchanger would sustain damage (e.g. where cracks would form that could lead to carbon monoxide leaks).

If your heating system’s fan limiter is not working properly, it will cause your furnace to shut off too soon.

The Fix

  • Check with a technician. If you’ve exhausted the other options mentioned in this article, you could ask your technician if your fan limiter could be the issue. (Your technician will also point out the issue to you if that is indeed what’s causing the problem).

7. The Furnace Is Too Big For Your Home

Lastly, another common cause for a furnace short cycling that you should consider is that your unit may simply be too large for the size of your home or business.

An oversized furnace will heat the space too quickly, shut off, and abruptly start again when the house cools down. This stopping and starting is not only annoying, but it also wastes energy and wears your furnace out faster than usual.

Furthermore, your home is never really a consistent, comfortable temperature. To prevent this from occurring, you should always check with an experienced furnace technician to ensure you have the proper furnace installation.

Read More: Signs Your Furnace Needs a Replacement

The Fix

  • Get a furnace replacement. The best solution is to replace your furnace with a correctly-sized, energy-efficient model, especially if it’s over 15 years old. Our HVAC technicians can help assess if your existing gas furnace is too large for your current space.
Furnace Short Cycling

Read More: What to Know Before Installing a New Furnace

Furnace Short Cycling FAQs

How to fix a short cycling furnace?

There are multiple reasons why your furnace is short cycling. These could include a dirty filter, blocked vent, or malfunctioning flame sensor. You can switch for a clean furnace filter, or have your HVAC technician resolve a more complicated issue. If you can’t diagnose why your furnace is short cycling, you should check with a trusted local technician.

Why is my furnace short cycling?

The most common cause of a furnace short cycling is due to heat becoming trapped in the HVAC system. This typically occurs whenever there is a malfunctioning air handler or a clogged air filter present. Without proper airflow, the system can’t pump out heat.

How to tell if furnace is short cycling?

While a well-insulated residence may have heating cycles that last as little as five minutes at a time, the sign that you have a short cycling furnace on your hands is if these cycles last a minute or two.

Furnace short cycling when cold?

When it’s cold outside, your furnace may turn on and off more regularly. The normal times your furnace will start and stop are between 3 and 8 times each hour, and if it’s just a few more times, chances are your unit is fine. However, if it’s much more than 3 and 8 times each hour, or if your furnace is barely running at all, you may want to call a technician to come take a look at your furnace.

Why does my furnace bang when it starts and stops?

Does your furnace bang when it starts and/or stops? Whenever your heating cycle stops, the sheet metal of the ductwork and the panels of your unit will cool and contract. This may result in a “bang” or a “pop” sound. A dirty air filter or blocked ductwork may contribute to the banging sound.

Furnace Short Cycling? Contact Us!

Have a short cycling furnace? Look no further than Modern Sheet Metal! Now that you know about some of the more common problems that can cause your short cycling furnace, you’ll be able to better evaluate the situation.

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As discussed in this article, some of these problems are something that an experienced or DIY homeowner can fix, but others are something that will require a experienced HVAC expert to remedy.

No matter if it’s a malfunctioning thermostat or a short cycling furnace, you can always rely on Modern HVAC for help. Our professional furnace repair or replacement specialists can help you determine what the root cause of your furnace issues are, give you a rundown of the furnace installation process, and how to properly maintain your furnace to prevent further short cycling issues.


Furnace Short Cycling: Area of Service

Is your furnace starting and stopping? If you’re dealing with a short cycling furnace, we also recommend routine furnace maintenance to ensure that your unit stays functioning well throughout the colder months, keeping you and your family warm all winter long!

We are the heating and cooling experts you can rely on in Appleton, the Fox Valley, and beyond! Here is our heating and cooling guide for more information about how to troubleshoot and care for your furnace. Beyond Appleton, we are happy to offer our heating and cooling services to Neenah, Menasha, Kimberly, Greenville, and Darboy.

Further Reading:

Modern Sheet Metal provides furnace and air conditioner service, repair, replacement and installation throughout Appleton, Neenah, Menasha, Darboy, Kimberly, Kaukauna and Greenville. Please call us at 920-733-4713 to discuss your residential or commercial heating & cooling needs!