What is a high-temperature limit switch on a furnace?
A limit switch is a device that’s located under your furnace’s supply plenum. It reads the temperature of the plenum and waits until it gets appropriately warm. Once the plenum reaches a specific temperature, the limit switch sends a signal to the air handler to begin running and delivering warm air to your home. A limit switch also acts as a safety device for your furnace. If …
What does the primary limit switch on a furnace do?
Mar 13, 2020 · What does a furnace high limit switch do? The limit switch is a safety switch that monitors the air passing over the heat exchanger and will shut the furnace off if the system overheats. If the high limit switch fails then the furnace might cycle on and off and will not function properly. The limit switch can be tested before replacing.
How do you test a furnace limit switch?
Jan 18, 2022 · A furnace limit switch is a device within your furnace that detects when the internal temperature is too high and turns the unit off as a safety measure. You may also hear it referred to as a fan limit switch or a limit switch. When your furnace is working correctly, you shouldn’t have to worry about your furnace limit switch.
What does limit circuit open mean on a furnace?
Mar 26, 2019 · What is a High Limit Switch? The high limit switch in your gas furnace is a small part with two very important jobs. This switch plays a role in the normal operation of your furnace. Turning the fan motor on and off is the high limit switch’s main job. This is the role it plays in every cycle of your furnace’s normal operation.
What happens when high limit switch trips?
What causes high limit switch on furnace?
Can you bypass a high limit switch on a furnace?
What is the most common use for a high limit switch?
Can you reset a high limit switch?
How much does it cost to replace a high limit switch?
You will need to buy a high limit switch that is produced by the same manufacturer as your furnace unit. Depending on who your OEM is, this component could roughly cost you anywhere from $4 to $25.Mar 11, 2021
How do you test a furnace limit switch?
Is a high limit switch normally open?
How many limit switches are in a furnace?
The mounting plate usually contains two or more terminals that receive control wires for the blower fan and the furnace's gas valve. It's possible that your furnace will have two or even three limit switches that check temperatures at different parts of the furnace.Nov 10, 2021
How do I know if my limit switch is bad on my furnace?
How do you reset a high limit switch on a furnace?
- Locate your furnace's heating duct. ...
- Locate the white limit switch. ...
- Look at each arm to identify the settings. ...
- Identify the component (setting) located in between the two arms. ...
- Set the temperature on the middle component to approximately 105 to 115 degrees Fahrenheit.
Why does my gas furnace keep short cycling?
Where is the limit switch on a furnace?
On some furnaces (usually older models), the limit switch mounts on the outside of the furnace rather than inside the service panel. These types usually have a rectangular cover plate that protects the wire connections.
What is a fan limit switch?
Also known as the fan limit switch or simply the limit switch, it has two functions in the furnace's operation: It turns the fan on and off during the normal heating cycles of the furnace, and it senses heat and shuts down the furnace if the interior temperature gets too high.
What happens if the limit switch doesn't shut off?
This happens when the switch fails to shut off after the burners have stopped and the air exchanger is sufficiently cool. A bad switch also can prevent a furnace from operating at all.
What happens when the thermostat calls for heat?
When the thermostat calls for heat, the furnace burners ignite and begin heating the heat exchanger. Initially, the air above the heat exchanger—in the supply plenum—is not warm enough to heat the house, so the limit switch keeps the blower off.
What is a high limit switch?
The high limit switch is also an extremely important safety device inside your furnace. When the furnace begins running, the switch’s role is to turn on the blower fan when the supply air gets hot enough.
What happens when a high limit switch goes bad?
One of the most common issues that happens when a high limit switch goes bad is that it fails to signal the blower fan to turn off.
Where is the blower fan switch located?
From the mounting plate, the switch is wired to the blower fan motor and to the gas valve. The switch is generally located just past the heat exchanger. This is so that it can detect the temperature of the supply air. In other words, the air that’s about to be blown into your home.
What happens if a furnace overheats?
This is a very important safety feature because if the furnace overheats, it can cause the heat exchanger to crack.
Why does my fan keep running?
If your fan keeps running continuously (and you’ve checked that your thermostat is set to AUTO rather than ON), that could be a sign of a bad high limit switch. High limit switches can also weaken over time so that they begin tripping at a lower temperature.
Why does my furnace overheat?
One of the most common causes of furnace overheating is a clogged furnace filter. So, in addition to regular annual maintenance on your furnace, regularly replacing your furnace filter is the best thing you can do to help your high limit switch last as long as possible. See Also: Contact Us.
What happens if a heat exchanger cracks?
And if the heat exchanger cracks, it can allow poisonous carbon monoxide gas to enter your home. By shutting off the gas valve, the high limit switch helps to keep your family safe, as well as helping to prevent costly repair or replacement of your system. See Also: Protecting Your Home From an Air Conditioner Fire.
What are furnace limit switches?
Furnace limit switches are electromechanical devices with momentary contact.
What is a high limit switch?
A high-limit switch is a protective part of a furnace designed to keep the mechanism from overheating itself. A furnace is at a risk of overheating any time airflow is limited from passing through the heat exchanger. A clogged filter or squirrel cage can limit the airflow and, without a high limit switch, the furnace would continually cycle until it burned itself out. The high limit switch shuts down the furnace at a set limit so a clog doesn’t burn out the system. Note that the limit switch has nothing to do with the thermostat. Rather, it is wired in series with the 24-volt control circuit of your furnace. A pair of wires is connected to the switch. When the furnace is cool enough, the switch closes, bringing the two wires together and setting the burner into action again.
What happens if a furnace is clogged?
A clogged filter or squirrel cage can limit the airflow and, without a high limit switch, the furnace would continually cycle until it burned itself out. The high limit switch shuts down the furnace at a set limit so a clog doesn’t burn out the system. Note that the limit switch has nothing to do with the thermostat.
How the Furnace High Limit Switch Works
A furnace high limit switch is an in-built safety mechanism that controls the opening and closing of the heating system. The switch will automatically shut off (close) when the furnace reaches an unsafe operating temperature.
What causes the furnace high limit switch to keep tripping?
A tripping switch in a gas furnace is a safety mechanism, but when it is erratic, it could be a sign some components of the furnace are not working properly. Oftentimes, tripping is because of one of three reasons: an inefficient furnace filter, faulty wiring or installation, or not enough airflow coming into the furnace.
How to Fix a Limit Switch that Keeps Tripping
The appropriate fix for a tripping high limit switch depends on the actual cause. It is important to diagnose the system first before attempting any of the repairs or fixes I’ve discussed below.
