Why Does My Furnace Keep Shutting Off?

Furnaces have to revolve through the complete circle to hit the temperature reading on the thermostat. Why does my furnace keep shutting off? If your furnace has a faulty component and doesn’t go through the whole cycle, it will stop halfway or quarterly. It will force the unit to turn on and off repetitively.

If the furnace continually turns on and off, it will take more hours to raise your indoor room’s temperature to the desired levels. It means more energy consumption and higher bills.

What’s My Furnace’s Cycle Like?

The first step to unmask the reason for your furnace to shut on and off repeatedly is to understand its cycle. The furnace cycle begins when you enter the temperature on the thermostat and then on the system. Once the thermostat sends the information to the furnace, the burner will start its magic of burning the natural gas to produce flames.

The heat exchanger will then transfer the heat to the air in your furnace. The hot air will then be pushed to your home’s ducting system by the blower fan.

As the hot air is transferred to the home indoors, the return vents will collect back cold air from your home, introducing it to the burner to complete the cycle. If the furnace fails to fulfill any of the processes, the cycle won’t be complete, and so it will turn off and on repeatedly.

What Causes The Furnace to Shut Off?

Different internal and external forces cause the furnace not to complete its cycle. Not completing the cycle means the system won’t heat your home, and if it does, it will take almost forever, translating to increased utility bills. The following are known issues that affect the furnace’s ability to complete the cycle.

Dirty and clogged air filters

Air filters take on the demanding role of cleaning the air flowing into your home. Days and weeks of sieving the air of pollutants and airborne dust will leave the air filters clogged and unable to stand up to their expected role in delivering quality airflow. Running your furnace when the filters are clogged will force it to shut down regularly.

The furnace has a safety mechanism that will detect inefficient air filters and signal the system to shut down. It will help avoid overheating issues. The simple solution to short-cycling problems caused by air filter clogging is to clean or replace them if they’ve been functioning for more than 90 days.

Dirty blower wheel

For the hot air to flow into the ducting, the blower will push it with the support of its blades. When the blower wheels get filled with dirty particles or dust, airflow will be affected, leading to short cycling and overheating.

The simple solution to avoid the blower wheels getting extremely dirty and failing is to clean them regularly. Regularly changing the air filters can also minimize instances when the blower wheels will get extremely dirty.

Problem with the thermostat

The thermostat doesn’t necessarily have to be faulty to read wrong temperatures. If you install the thermostat in an area that receives lower or higher temperatures, it will fail to read the correct temperatures because the external temperature will affect its accuracy.

When the thermostat reads wrong temperatures, it will send the incorrect information to your furnace. The inaccurate temperature readings will make the furnace unable to complete each cycle, leading to repetitive on and offs.

The same will be the case if your thermostat is faulty or has drained off batteries. Before hiring an HVAC technician to inspect and repair the thermostat, check out if the batteries are drained out.

Larger than normal furnace

If you install a furnace bigger than your home’s heating needs, it might as well keep shutting on and off. Bigger furnaces heat smaller spaces faster and shut off quickly, leaving the area to cool off faster than expected. The furnace will then shut on once the temperature has gone below the desired room temperature.

That often makes the furnace follow a short cycle that will strain it instead of heating your home correctly. The solution to furnaces that keep turning on and off is to buy a furnace that meets your home heating needs.

Corroded or soot-covered flame sensor

Your home furnace will also succumb to the short-cycling if the flame sensor gets covered by soot. The flame sensors detect when the there’s an ignited flame and shut off the furnace gas valve if it doesn’t sense any flame. It serves a security role of preventing instances when your home contains harmful gas fumes that are a serious health hazard.

It’s an integral component in the furnace that works tirelessly to ensure your home is comfortable and safe. However, when the flame sensor gets soot-covered or corroded, it won’t effectively detect flames and always put off the gas valve. It will keep short-cycling and shutting on and off, so it won’t heat your home.

Can the Repeated On and Off of My Furnace Damage It?

If the furnace keeps shutting on and off, you shouldn’t ignore it. Short-cycling puts the furnace in a working pattern different from the standard one, which might strain it and cause the failure of essential components. If there’s no immediate action on an unsolved problem, the strain will continue, reducing the furnace’s life.

If your home heating system starts turning on and off in a repeated pattern, you should shut it off and call your HVAC technician. A thorough system checkup enables the technician to tell what’s causing the short-cycling and offer a long-term solution to cut you the hassles and costs.