One of the most common malfunctions that homeowners deal with in their furnace is short cycling. This is described as your furnace frequently cycling on and off. This problem is not only frustrating, but it can increase your energy bills, lead to uneven heating, and prematurely wear out your furnace’s internal components.
What Is Short Cycling?
Your furnace is specifically designed to turn on two to three times per hour and run until your home reaches the temperature set on your thermostat. A typical heating cycle lasts anywhere between 10 and 15 minutes, depending on multiple factors like your home’s insulation level and the weather. Short cycling happens when your furnace turns on, only runs for a few minutes or even seconds, and then shuts back off.
The Problems Associated With Short Cycling
While short cycling may seem like a minor inconvenience, it can create long-term damage. One of the first areas you’ll notice is higher energy bills, as your furnace uses a high amount of energy to start up. As it repeatedly tries to start over and over again, it will consume excessive amounts of energy compared to what it normally uses.
This constant starting up and shutting off is highly demanding on your furnace’s internal components. Constantly restarting puts stress on them and can lead to breakdown and increased wear and tear. Some of the most common components to be overly stressed due to frequent cycling include your ignition system, blower motor, and heat exchanger.
Another problem with short cycling is that it can lead to uneven heating throughout your home. This is because your unit shuts off before it can complete a full heating cycle that will produce enough heat to comfortably warm up all the areas of your home. With all this increased stress on your unit, it’s likely to have a much shorter lifespan by several years compared to a unit that gets prompt repair service.
Dirty Air Filter
One of the most common culprits of furnace short cycling is a dirty air filter. Whenever your air filter gets clogged with debris, it will restrict airflow throughout your ductwork. This means all the heat your furnace produces lingers in the furnace. This causes it to overheat, and its high-limit safety switch will automatically shut off the furnace. This is done in an attempt to prevent any major malfunction, such as a fire.
Once your furnace cools back down, it will kick back on to try to repeat the cycle. The good news is that having a dirty air filter is fairly easy to remedy. All you need to do is remove the dirty filter and replace it with a new one. Ensure that you’re using the appropriate size filter for your unit. It’s a good rule of thumb to check your air filter every month and replace it whenever necessary. Most homeowners find they need to replace their furnace filter about every two to three months.
Overheating Furnace
While a dirty air filter is the most common cause of an overheating furnace, there are many others. Having enclosed or obstructed return registers can mess with the air pressure in your ducting and prevent air movement. Having dirty blower components can also be to blame. Any time that your furnace overheats, it automatically shuts down as a safety precaution.
It’s a good idea to always check to ensure that all your supply and return vents are completely open and unobstructed from things like furniture, rugs, or even curtains. It’s a good idea to consider professional duct cleaning every three to five years. This removes any buildup of debris inside your ducting that could otherwise lead to short cycling issues.
Thermostat Malfunction
One component that’s commonly overlooked, when it comes to short cycling issues, is your thermostat. If your thermostat is incorrectly placed near vents, windows, or heat sources, it could falsely shut off your furnace before it gets through a whole heating cycle. If it has loose wiring, dead batteries, or poor calibration, it can also cause your furnace to intermittently turn on and off. You can try replacing the batteries in your thermostat if they’re dead. However, it’s important to have a professional do a more thorough evaluation to determine if there’s an issue with its calibration, wiring, or the thermostat itself.
Oversized Furnace
If you’ve recently replaced your furnace and started having this issue, it could signal that you have a furnace that’s too large for your home. The mentality that bigger is always better doesn’t hold true when it comes to furnaces. If your furnace is too large for your home, it will raise the temperature too quickly and cause the furnace to shut off. This results in repeated short cycles, which leads to inconsistent comfort throughout your home. Unfortunately, the only way to repair this issue is to replace your furnace with a smaller one that is better suited for your home’s unique size.
Flame Sensor Problems
Furnaces that burn fuel to create heat have a built-in safety mechanism known as a flame sensor. This works to ensure that gas can freely flow to your burner whenever there’s a flame present. Any time that the flame sensor detects that there’s no longer a flame on the burner, it will automatically shut off the fuel supply. This is to prevent a buildup of toxic gas inside your unit.
If your flame sensor is malfunctioning, it could be falsely shutting the fuel supply valve when it’s unnecessary. This can happen when the flame sensor eye gets dirty and can’t see the flame on the burner. It can also happen when the flame sensor itself is faulty and in need of replacement. It can be helpful to have one of our technicians thoroughly clean and test your flame sensor.
Blocked Exhaust Vent
Furnaces that burn fuel have an exhaust vent that removes toxic fumes from the combustion process to the outdoors. If that exhaust vent becomes blocked with snow, ice, leaves, or other debris, it can prevent your furnace from operating properly. Your furnace will shut down due to overheating and safety reasons. This is what causes the frequent cycling. It’s important to remove any debris from the exhaust vent before turning your furnace back on.
Faulty Limit Switch
Another common culprit of furnace short cycling is a faulty limit switch. Limit switches are responsible for monitoring the temperature of your furnace and shutting it off whenever the temperature gets too high. This is to prevent damage to the internal components of your furnace and prevent fires. If the limit switch is malfunctioning, it could falsely detect that your furnace is overheating and shut it off repeatedly. It’s important to have one of our technicians do a professional diagnosis of your unit and replace the faulty limit switch.
Expert Furnace Repair Service
Summit Heating, A/C, Plumbing & Electrical provides expert furnace repair service in Denver, CO. We can also help with all your heating tune-up, replacement, and new installation needs.
Give us a call today to book your next service appointment with one of our friendly technicians.
