4 Possible Reasons Your Gas Furnace Keeps Shutting Off

Having your gas furnace suddenly shut down before it has time to fully heat your home can be frustrating. This issue is known as short cycling, and it can occur for a variety of different reasons. No matter the specific cause, it is something you will want to get taken care of immediately, as it always leads to higher energy costs, a lack of sufficient heat, and greater wear and tears on the furnace and blower fan. Let’s look more closely at the reasons that this problem can happen and what steps you can take to overcome each potential cause.

1. Overheating Caused by Insufficient Airflow

One common reason that a gas furnace will shut down too quickly is due to overheating. All gas furnaces have something known as a limit switch that constantly measures the temperature of the furnace and the blower fan whenever the heating system is running. If the limit switch ever detects that the temperature is too high, it will automatically trigger the furnace and blower to shut down. Once this happens, the system won’t turn on again until the limit switch detects that everything has sufficiently cooled. The limit switch is an essential safety component as overheating can cause major damage to the furnace and also create a fire risk.

The most common cause of overheating is insufficient airflow. Whenever the heating system is running, the blower fan is constantly drawing cold air into the furnace. This cold air is forced over the furnace’s heat exchanger, which works to both cool the exchanger and heats the air. If there isn’t enough cold air coming into the system, much of the heat will remain trapped inside the furnace causing the heat exchanger to quickly become extremely hot and leading to the furnace overheating. Insufficient airflow also causes the blower fan to work much harder, and this can also lead to its motor quickly overheating and the system shutting down.

Insufficient airflow can occur for a few different reasons, the most common of which is a dirty air filter. When the air filter becomes clogged with dust, hair, and/or debris, it severely restricts the amount of air that can flow through it. To prevent this, all you need to do is make sure to replace your air filter once every one to three months.

Other issues that can lead to insufficient airflow include dirty ductwork, damaged or leaking ducts, and closed or obstructed vents. If there is lots of dust and debris in the ducts, it increases the static pressure or resistance to airflow and will force the blower fan to work much harder to circulate air throughout the system. The same can also happen if there are a lot of gaps or air leaks in the return ducts or if too many of your supply vents are clogged or obstructed by furniture. Similarly, closing too many of your supply vents can also lead to an increase in static pressure. To avoid this, it is recommended that you always have at least 75% of the vents open.

2. Dirty Flame Sensor

Most furnaces have something known as a flame sensor, and this sensor is what controls the flow of gas into the unit. As you might expect, the flame sensor works by detecting whether the furnace is lit. If the sensor doesn’t detect a flame within a few seconds of the furnace turning on, it will automatically close the gas valve. This causes the furnace to instantly shut down as a safety precaution to ensure that gas can’t fill the furnace when it’s not lit.

The flame sensor can sometimes malfunction, in which case it will need to be replaced before the furnace will work properly again. However, the most common reason that a flame sensor stops working is that it is coated in soot and grime, which can prevent it from properly sensing the flame. The easiest way to avoid this issue is with annual furnace maintenance as the technician will always clean the flame sensor and test to make sure it is working correctly.

3. Malfunctioning Thermostat

In some cases, the issue isn’t related to the furnace itself and instead due to some problem with the thermostat. One possible cause is that the batteries in the thermostat are starting to go dead. This can lead to the thermostat only working intermittently and can cause the furnace to shut down if it’s not receiving a signal from the thermostat.

Another possibility is that the thermostat isn’t accurately measuring the temperature. The location of the thermostat can play a major role in this issue, as there are certain factors that can interfere with its ability to accurately gauge the temperature. For instance, if the thermostat is within a few feet of a supply vent or in an area that is warmer than the rest of the home, it will always register a temperature that is higher than the actual temperature in the rest of the building. This will lead to it signaling the furnace to shut down quickly before it can fully heat the building. The same can occur if the thermostat is in a location where it receives direct sunlight.

When choosing the location for a thermostat, it is always best if it is in a central part of the building in a room that you use frequently, and that gives an accurate representation of the temperature throughout the home. It should also be in a place with good air circulation, which is why hallways are usually a bad choice. Luckily, having your thermostat moved is a fairly simple task, one that can pay huge dividends for both your heating and air conditioning systems.

4. Oversized Furnace

The saying that bigger is always better may be true in some situations, but definitely not when it comes to furnaces. An oversized furnace will produce too much heat too quickly and this will almost always lead to short cycling. In this situation, the blower fan simply can’t circulate enough air and the furnace will begin overheating within a few minutes of turning on. This is why it is essential that you always hire an experienced, certified HVAC contractor whenever you need to replace or install a new furnace as they will perform a number of calculations to determine exactly what size of unit you need.

Unfortunately, if your current furnace is oversized, the only real solution is to replace it with a unit that is the proper size for your home and your climate zone. While this is a major expense, it is also necessary, as oversized furnaces typically have an extremely short lifespan and need more frequent, potentially costly repairs.

Western Michigan’s Heating and Cooling Experts

If your furnace is frequently shutting off too soon, the certified technicians at Bel-Aire Heating & Cooling can inspect it and your entire heating system to determine why and how to overcome the issue. We offer professional furnace maintenance and repair services, and we can also help with replacements and new equipment installations. Our team also installs and services boilers, air conditioners, mini-splits, geothermal HVAC systems, and indoor air quality units, and we serve both residential and commercial customers in Grand Rapids, Portage, Three Rivers, and across Western Michigan. Contact us today if you have any questions or need a furnace inspection.

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