As winter approaches, questions about furnaces start to increase. With that in mind, we are starting a monthly Furnace 101 blog that will detail the parts and functions and give you more information you probably never wanted to know about your heating system. Today, we are diving into a small but very important part of your residential furnace: the furnace limit switch. A switch that most furnace owners do not even know exists within their heating system but is essential in the normal operation of your forced-air furnace that keeps your Toledo, OH home warm on a cold winter’s night.
What is a furnace switch?
A furnace switch is located in a forced-air furnace, and its sole job is to turn on the furnace blower once the furnace has warmed up enough to move warm air through the home. This switch works with the thermostat to keep your home comfortable and prevent it from getting too hot or too cold. Generally, these switches are slightly larger than a silver dollar and include an exterior plate and a temperature probe inside your furnace housing.
How does this switch regulate the temperature?
When your thermostat calls for heated air, the furnace starts heating. This process takes a few minutes, but once the furnace reaches the set temperature, the limit switch closes and turns on the blower to move heated air through the duct system. Once your space reaches the temperature indicated on the thermostat, the furnace heating element will turn off. Still, the blower will continue moving air through the home until the furnace temperature drops below the threshold. Depending on the home's temperature, the heating element may kick back on, and the switch will activate when it reaches the ideal temperature, or the system may stay off for an extended time.
Is the switch important for other aspects?
Yes, the furnace limit switch does more than regulate your furnace temperature; it also helps ensure your furnace isn't running too hot or getting out of control. An overheated furnace might seem like a minor problem, but residential furnaces are designed to work within a specific range, and when they exceed that range, issues can start to pile up. The most common issue is a blower fan malfunction. The furnace limit switch can help prevent this damage from happening in the first place.
Is the Furnace Limit Switch related to the Furnace Pressure Switch?
If you have been in your furnace before, you may have noticed a similar-sized and looking switch called the furnace pressure switch. This switch is certainly related to the limit switch, but it does a separate job within the furnace. The furnace pressure switch detects negative pressure in the unit and shuts down the furnace immediately if it detects it. Negative pressure, also known as a backdraft, can be dangerous because toxic combustion gases, including carbon monoxide, can be pulled into the blower and distributed through the air ducts.
What happens when a furnace limit switch malfunctions?
If a furnace limit switch malfunctions, one of two things will happen. First, the furnace fan will run nonstop and will not turn off unless you cut power to the unit. Second, the furnace fan will not turn on, even if the unit has reached the ideal heating temperature.
Can you replace your furnace limit switch yourself?
In theory, you can replace the furnace limit switch, but most furnace owners should call a professional HVAC company. A heating and cooling technician can confirm whether the switch is the issue, provide a replacement, and service and inspect the furnace. Most of the time, a new switch will fix the problem, but for some furnaces, a technician will need to check other components that may have failed as well to get your furnace running again.
The furnace limit switch is one of the most important components of a functional and effective furnace. Your furnace needs to regulate temperature, and a proper switch keeps it running safely without increasing the risk to other internal components. It is a small component, but a mighty one. If you're having furnace issues or want a full checkup to make sure your unit is in working order, now is the time to call Fry Heating and Cooling, the certified HVAC experts in Toledo, OH. From small replacements like a furnace limit switch to a full system rebuild, our local heating and cooling experts can get your furnace back up and running without breaking the bank.
