Do you ever wonder how your furnace works? There are many components inside that heat-producing appliance.
One of these parts is the furnace limit switch, also known as a furnace high limit switch or furnace fan limit switch, and without it, your furnace could put your family in danger.
So what’s the proper working of this small switch? Keep reading to find out.
What Is A Furnace Limit Switch (In heating systems)
A limit switch can be found under the supply plenum of your furnace. It monitors the plenum’s temperature and waits until it becomes warm enough. When the plenum approaches a certain temperature, the limit switch tells the air handler to start delivering warm air to your home.
You can also use a limit switch as a safety device for your furnace. When the specified temperature inside the plenum gets too high, the gas supply is shut off so that your furnace and heat exchanger do not overheat.
What Does A Furnace Limit Switch Do
Furnace fan limit switches are designed to turn the furnace blower assembly on and off. This component aims to distribute warm air throughout your home’s air ducts. Also, the furnace limit switch ensures that the furnace won’t overheat because it shuts it down when it reaches a certain temperature.
Need Of A Furnace Fan Limit Switch
Furnace Limit switches ensure that your furnace does not become too hot throughout the standard operating cycle. This feature helps prevent damage to your furnace’s internal components and keeps your family safe. Additionally, the furnace fan limit switch is responsible for keeping your home at a comfortable temperature and eliminating drafts.
Furnace Limit Switch Looks Like
A forced air furnace limit switch is connected to furnace plenums inside the cabinet. Mounting plates have a long temperature sensor probe attached to them. This mounting plate is fastened outside the furnace’s plenum but inside the furnace cover, and the probe enters the furnace’s plenum through the furnace housing.
The mounting plate is attached to the blower fan and gas valve wires. The location of the limit switch varies by make and model but is usually attached to the plenum above the combustion chamber and/or heat exchanger.
How A Furnace Limit Switch Operates
Your furnace thermostat begin heating the plenum when it detects the household temperature is too low, and your furnace burners are ignited. A fan limit switch, activated when the plenum air is hot enough, causes the blower assembly to blow the heated air past the heat exchanger.
Using the house’s air duct system, the warm air will circulate in every room. The thermostat turns off the furnace once it recognizes your home is sufficiently warm. As long as the internal furnace temperature is low enough, the blower will keep on running, once it reaches the threshold temperature limit switch shuts down.
When a furnace burner continues to run even when the system itself does not work properly or breaks, the high limit switch will shut off the gas valve to prevent fires or other dangers.
Furnace Limit Switch Regulates Temperature
The thermostat signals the furnace when the heat is turned on or increased. The furnace limit switch closes when the furnace heats up, closing the circuit and turning on the blowers.
The furnace will shut off the burners once the desired temperature is reached. However, the blower will continue to run until the temperature inside the furnace reaches the lower limit (the coolest air temperature permitted by the thermostat).
The unit may cycle and re-start or remain off for a long time, depending on how warm the air inside the house is. This high-limit switch allows the furnace to operate more efficiently.
The thermostat sends a signal back to the furnace to kick on, which begins the cycle as the home cools.
A problem with the blower fan can cause overheating, or when a dirty furnace filter restricts airflow through the exchanger and furnace, causing it to overheat.
Furnace Limit Switch Stops Working Properly
Your furnace’s limit switch can develop problems over time. Airflow issues in your system most commonly bring on these problems. With the lack of proper airflow in your furnace, like operating with a dirty filter, your heat exchanger will repeatedly overheat and put your limit switch through excessive wear and tear. The limit switch may eventually fail.
No matter what the cause, a malfunctioning limit switch will cause problems with your system. You may find that your air handler doesn’t turn on during the heating cycle of your house if the limit switch isn’t sending a signal. If your limit switch fails to shut off the gas to your burners at the right time, your furnace could overheat without shutting down.
Signs Of Limit Switch Is Failing
What are some signs that a limit switch is failing? The furnace safety switch can stop abruptly or run short cycles and exhibit two other signs. In the first instance, check to see if the furnace blowers aren’t shutting off when they should. Furthermore, if the air coming from the vents is cool and not warm, that is another sign.
This is a good sign that the system is working and that you are protected. You need a furnace that produces warm air safely and reliably in the winter months.
Common Problems With Furnace Switches
It is not uncommon for the furnace fan limit switch sensor to malfunction as the furnace gets older. The fan limit switch should be cleaned of all dirt, grime, and other materials that may prevent your furnace from working correctly from the fan limit switch.
If your furnace constantly activates and deactivates throughout the day, a problem with the blower motor may be to blame. Overheating a blower assembly will trip the furnace limit switch, which will cause the furnace to deactivate before the end of a standard heating cycle.
Other common problems affecting the furnace fan limit switch include faulty gas valves, thermostats, and electrical circuits. Finally, we always recommend checking the furnace’s filter to ensure it is not blocked. If your furnace’s air filter is clogged, it may cause the plenum to reach dangerous temperatures. Once the plenum overheats, the furnace limit switch will turn off the furnace to keep you safe.
Can I Replace A Furnace Fan Limit Switch
You can follow these steps to replace your broken or worn-out furnace limit switch and save yourself several hundred dollars from paying other local contractors.
Furnace Deactivation
Disconnect your furnace’s power using the switch or the circuit breaker. Taking this precaution will ensure no safety accidents occur during DIY replacement.
Removal & Configuration
Remove the high limit switch from the furnace cabinet after switching off the furnace. Install a new switch and wire it exactly like its predecessor. Two screws, wires, and terminals are usually all that is needed. Follow the instructions to ensure that the dial settings remain the same or are adjusted accordingly.
If your model is older, read the installation instructions for assistance following the small additional steps, including wiring the third line, installing a tab switch, and setting the dial accordingly.
Operational Testing
After configuring the furnace limit switch, turn the furnace on and adjust the thermostat to start the heating system. Verify that your vent is blowing out sufficient warm air and that nothing seems out of the ordinary to confirm your successful switch replacement.
When To Contact An HVAC System Expert (When to get your furnace limit switch inspected)
A preventive maintenance program cannot be overestimated. If you change your furnace filters regularly, you can ensure that your furnace stays in good working order. However, you may also want to consider periodic professional service. An HVAC unit professional can clean and inspect your furnace and, in the process, spot any minor problems before they become major ones.
Finally, suppose your furnace seems to be operating differently for reasons you can’t explain, such as a sudden drop in outside temperature causing it to cycle on more frequently. In that case, you must contact a limit switch HVAC specialist. The first thing they can do is address any safety issues with your system. In addition, it can be cost-effective to do so.
Replacing or repairing a faulty system component before it damages other components is much more cost-effective than performing a major repair later. Additionally, if your furnace is operating inefficiently, you are likely paying more to keep your home or business at a comfortable temperature.
Cost Of Furnace Limit Switch
Your furnace unit must be equipped with a high-limit switch produced by the same manufacturer. You can expect to pay between $4 and $25 for this component. You may also find a universal switch on the lower end of this price range, but we encourage you to consult your furnace manufacturer to determine whether it would work in your model. If you looking to change the furnace limit switch then contact Deep Clean NL for top quality services.
Conclusion:
A furnace limit switch is a safety device that helps to protect the furnace from overheating. It does this by shutting off power to the furnace if it senses that the temperature has exceeded a certain level.
This switch is important for keeping your home safe and preventing damage to your furnace. If you have any queries about your furnace limit switch, be sure to contact one of the furnace repair services because it’s a matter of your safety.