Why Your Furnace Is Short Cycling - Cause, Troubleshooting And Fixes

Why Your Furnace Is Short Cycling - Causes, Troubleshooting & Fixes

A furnace can make a house cozy in the winter by raising the temperature inside to a comfortable level, but when it malfunctions, it can make for an uncomfortable experience for anyone inside.

When a furnace short-cycles, it starts up, runs for a short period, and then turns off before the house has had a chance to get sufficiently warm. On the other hand, a smoothly working furnace will work so that it first switches on and increases the room's temperature to the one you’ve set on the thermostat. A normal furnace system will turn off automatically once its temperature sensor tells it that the room has reached the temperature it was set to. Numerous problems can be to blame for short-cycling.

Short-cycling, on the other hand, is not only uncomfortable, but it can also lead to bigger problems. For a variety of reasons, short-cycling is bad:

  • First off, rather than running continuously, the furnace starts up and shuts down several times throughout the day, which can be quite inefficient. Consequently, your energy bills can go up.

  • Second, short-cycling puts the furnace under additional stress, which could cause it to age prematurely. This may reduce the furnace's lifespan and raise the possibility of expensive repairs.

  • Finally, short-cycling may indicate a more significant furnace issue, such as a component failure or a gas leak. These problems could possibly be dangerous if they are not resolved.

It is possible that nothing could be more irritating than a short-cycling furnace system that never lets the room get warm enough for you to relax. This furnace problem can be a pain for many owners who just want their furnace to keep them warm. To better understand this issue, some reasons for a short-cycling furnace are listed below.

Furnace Short Cycling Causes - Why Your Furnace Is Short Cycling

Overheating Furnace - Furnace Short Cycling Causes

Overheating is one of the most common and dangerous causes of a faulty furnace system. If your furnace is overheating by itself, it could be that the temperature monitoring components inside your furnace are working improperly. 

An overheated furnace system can create cracks in your heat exchanger. The heat exchanger usually contains dangerous combustion fumes, including carbon monoxide, which could spread outside the furnace through the cracks. This is why you should be careful with an overheating furnace system.

Solution: If your furnace is overheating, it is usually best to call a technician right away, as this is a serious problem. Getting hands-on with your unit at a time like this can do more harm than good. Your heat exchanger or another part that controls the temperature might need to be fixed or replaced.

A Bad Flame Detector - Furnace Short Cycling Causes

Furnaces have a safety feature called a flame detector that is used to find out if there is a flame on the burners. The flame detector is an important safety feature because it makes sure the furnace works well and safely.

The gas supply to the burners will be cut off if the flame detector doesn't detect a flame when it should, which will stop the furnace from operating. The accumulation of dangerous quantities of carbon monoxide in the house, which can be harmful or even fatal if inhaled, can be averted with its use.

The flame detector, which is normally placed close to the burners, is triggered when it detects the ultraviolet or infrared light given off by a flame. The gas supply will be cut off if the flame detector doesn't detect a flame, which will stop the furnace from operating.

A broken flame detector could cause a dangerous situation, so it is very important to make sure it is in good shape. A flame sensor might also deteriorate in its functioning if it hasn’t been cleaned well enough.

A malfunctioning or dirty flame detector can cause a furnace to run ineffectively.

Solution: Regular inspection and cleaning should do the trick for a bad flame detector. It’s possible that your heat sensor is being blocked off by dust and debris. It could go back to working properly once cleaned.

The following are the steps for cleaning a flame detector:

Step 1: To clean the flame sensor rod, start by looking for a high-limit switch. It is often fastened to the outside of the furnace plenum with a metal plate that is screwed on. A large metal box called a furnace plenum is where the air is heated.

Step 2: To find a high-limit switch, remove the furnace cover.

Step 3: Take out the two screws holding the rod to the plenum so you can clean it on your own.

Step 4: Gently scrub it with steel wool or sandpaper.

However, it is also possible that the small amount of water released near the flame sensor might have caused it to corrode. This could have deteriorated the sensor itself, so simply replacing the flame sensor may be a good idea.

Dirty Furnace Filter - Furnace Short Cycling Causes

A dirty filter can also lead to overheating your furnace and, ultimately, short-cycling. When an air filter is clogged up or contaminated, it reduces the amount of airflow from outside that enters the furnace system. This means that there is no new air for the system to heat. 

On the other hand, the warm air inside the furnace is held back instead of being sent out to heat the room. This process is called "backup," which will cause heat to accumulate inside the walls of the furnace and ultimately lead to overheating of the unit. Finally, the unit will start short cycling to protect itself from releasing dangerous gases.

Solution: For a dirty air filter, clean or replace it—and not just when you run into a problem like this but monthly and yearly. There is a reason air filters are designed to be washable and reusable.

They help keep the unit in good shape; if they are cleaned on time, the internal parts will stay safe, and only clean air will come out for you to enjoy. If you have been using the same furnace filter for way too long, it is subject to wear and tear. In such cases, it might be a better idea to replace it.

Faulty Thermostat - Furnace Short Cycling Causes

The thermostat is the most important part of a heating and cooling system because it lets you set and keep the right temperature in your home or place of business. It can be set to vary the temperature at different times of the day or night, or it can be set to a specific temperature. 

So then, of course, one of the leading causes of a faulty furnace is a faulty thermostat. Thermostats have many (often technologically integrated) components that can lead to their malfunction or failure.

However, if your thermostat isn't working properly, it's causing your furnace to malfunction. As we often forget, it is sometimes simply a matter of ensuring that your furnace is set to heating mode.

Solution: If you have a faulty thermostat, it should be troubleshooted and repaired or replaced. Usually, a simple repair works for thermostats, but sometimes the issue can be complex.

Check out our Why Your Thermostat Not Reaching Set Temperature? Causes, Troubleshooting & Fixes for some DIY solutions, or reach out to your local HVAC service and have them come to troubleshoot your air system.

Oversized Furnace - Furnace Short Cycling Causes

If your furnace is even a bit oversized for your house, there’s a chance that it is going to malfunction. This is because furnaces, like air conditioners, have a set area that they can heat accurately and thoroughly. 

A furnace that is too big for your home might heat up your room quickly and inadequately because it aims to keep the temperature even throughout your home. 

This often leads to short cycles and temperature swings. In the case of an oversized furnace, the best option is to go for a full replacement, but talking to your HVAC technician before making any decisions might yield the best results.

Additionally, if your house isn’t well insulated, that is, if it has cracks and gaps that haven’t been sealed, heat will likely escape out of your room too quickly, which will also cause the furnace to switch on and off too quickly.

Solution: As discussed, the best solution for a furnace that is too big might be simply replacing it. This is because it is likely that you will keep running into problems if you stick with a furnace that is simply unsuitable for your home.

There are companies out there that will help run tests and see if your furnace is truly incompatible with the house. So, you can always contact them to be sure before making any decisions.

Misplacing The Thermostat - Furnace Short Cycling Causes

You might not even realize that this was the reason behind your furnace’s short cycling, but a poorly placed thermostat might sneakily sabotage your furnace’s work.

This is because your thermostat might be located where temperatures are higher, and thus, it’s being heated up way before the rest of the house. 

This leads to the device sending back a reading to the furnace of its own temperature, causing the furnace to shut off, assuming the house has reached its set temperature.

This phenomenon is especially common with thermostats that the owners themselves have set up. If your thermostat is set up above a heating grate, in a utility closet, or close to a lamp or a tube light, it’s likely that this is where the problem lies.

Solution: If you’re dealing with a poorly located thermostat, the most obvious solution is to place it somewhere else. Or, if you can, you can shift moveable heat sources like the lamp and put them out of the way. It is recommended that you put the thermostat in a location that isn’t subject to sunlight or air from the heat grate.

Safely Performing Maintenence on Furnaces - Why Your Furnace Is Short Cycling

Before you do any work on your furnace, turn off the power switch and the circuit breaker. Before working on an electrical item, you should first make sure that it is turned off.

For several reasons, a furnace should always be shut off prior to maintenance:

  • The furnace could emit sparks that could be fatal if it isn't turned off. These sparks have the potential to ignite items in the furnace and start a fire.

  • Before using a furnace, it should be turned off, because if it isn't, an emergency could happen and you wouldn't have time to get away. If there's a fire in the furnace, the heat and smoke will make it impossible for you to escape in time.

  • Electric shocks can also be extremely harmful.

You shouldn't work on a furnace when the electricity is on since the results could be fatal.

Furnace interiors can be hazardous, not to mention how filthy they frequently are. The most crucial safety equipment to wear when working inside a furnace is a dust mask and goggles. Gloves, long pants, and a shirt that protects your arms are also recommended.

Make sure you have the right equipment before performing furnace maintenance.

There is no shame in asking for help if you lack the necessary tools or are unsure of your ability to solve the problem. If you require assistance with repairing your air system, get in touch with a nearby HVAC business.

Conclusion - Why Your Furnace Is Short Cycling

Overall, living with a short-cycling furnace can be incredibly uncomfortable. Because your furnace is working so hard, it shortens its lifespan while failing to provide you with the comfort you were promised. Because of this, you should examine and repair your furnace as soon as possible so you may continue to enjoy it.

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