Where is the high limit switch on an electric furnace?
The high-temperature limit switch is typically located in the hot-air supply plenum which is above the furnace’s combustion chamber or heat exchanger. However, it varies with the furnace model. If you can’t find it, knowing your furnace’s model will help you do some online research to determine where it is.
How to reset limit switch on furnace?
Where is the Furnace Fan Limit Switch Located?
- Turn off the furnace Switch the furnace off at the circuit breaker. Then switch off the power at the furnace too.
- Remove the access panel Most panels come off without removing any bolts or screws. ...
- Locate the fan limit switch The switch is mounted on the furnace air plenum and is easily recognizable due to the wiring. ...
Where is the Furnace Fan limit switch located?
Your fan limit switch is located inside the furnace panel cover, usually near the upper right corner. The fan limit switch is responsible for turning the blower on and off at the appropriate times.
What is a high-temperature limit switch on a furnace?
A high-temperature limit switch also called a fan limit switch or simply a limit switch is an important device used in forced-air furnaces powered by gas or heating oil. Simply put, it senses the temperature of the furnace and tells the blower fan to turn on and off at the appropriate times .
How do you reset a high limit switch on a furnace?
You can try resetting the furnace limit switch yourself if you have a newer model by turning off the furnace for 30 seconds and then turning it back on. However, if this does not work or the furnace repeatedly shuts down, calling heating experts to reverse or reset the limit switch is a good idea.
What does a furnace high limit switch look like?
2:1618:59HVAC Furnace Short Cycling - How High Limit Switch Works - YouTubeYouTubeStart of suggested clipEnd of suggested clipIf it starts getting too hot this normally closed little switch will open up and interrupt the powerMoreIf it starts getting too hot this normally closed little switch will open up and interrupt the power which will effectively turn off the gas burners or the heating element.
How many high limit switches are on a furnace?
It's possible that your furnace will have two or even three limit switches that check temperatures at different parts of the furnace. The terminals for these switches may each have their own mounting plate, or they may be part of a single combination unit.
How do you know if a limit switch is bad?
The most common sign of a malfunctioning limit switch is the continuous operation of your furnace's blower. Just as the limit switch won't allow the fan to turn on until the warm air has reached the right temperature, the limit switch also shuts down when the air cools to a certain temperature.
Where is furnace reset button?
All furnaces are equipped with a reset button. They are generally red or yellow and are located inside the blower compartment. The reset button is a safety feature that will shut down the furnace when a problem is detected, often a hot or overheating furnace, before it trips the circuit breaker.
How much does it cost to replace a limit switch on a furnace?
This component could cost anywhere from $4 to $25, depending on your original equipment manufacturer. At the lower end of this price range, you might like to buy a universal switch.
Can you run a furnace without a limit switch?
A furnace limit switch is a component of a forced-air furnace that is responsible for turning on the furnace blower once the desired heat has been met inside the furnace. Without a functioning furnace limit switch, a furnace would not be able to regulate the temperature in conjunction with a thermostat.
Can you clean a high limit switch?
Remove the high limit switch by removing the two screws that hold it to the plenum. If the flame sensor rod is dirty, you can try cleaning it gently with steel wool or sandpaper, or replace the part with an identical new part.
Can I bypass a high limit switch?
Yes, you can bypass the high limit switch for testing.
Why does my furnace keep shut off before reaching temperature?
A lack of airflow can cause your furnace to stop heating before reaching the set temperature. Ensure there is nothing impeding airflow around your furnace, within your furnace and through your ducts. Check that registers are open, no ducts are damaged or crushed and replace your furnace filter.
How do you test a heat limit switch?
0:115:37Quickly Testing Gas Furnace Safety/Limit Switches! - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo right here we have our flame rollout switch we have another flame rollout switch right here weMoreSo right here we have our flame rollout switch we have another flame rollout switch right here we have a thermal limit switch. And i'm going to show you how to test those with your multimeter. To test
What is the purpose of a limit switch in a warm air furnace?
The furnace fan limit switch is designed to activate and deactivate the furnace blower assembly. This component is responsible for transmitting warm air throughout the air ducts in your home. In addition, the furnace limit switch is also engineered to shut down the furnace to ensure it doesn't overheat.
Can you bypass a high limit switch?
Yes, you can bypass the high limit switch for testing.
Can you clean a high limit switch?
Remove the high limit switch by removing the two screws that hold it to the plenum. If the flame sensor rod is dirty, you can try cleaning it gently with steel wool or sandpaper, or replace the part with an identical new part.
What does a furnace pressure switch look like?
A furnace pressure switch is a safety device located near the draft inducer motor of a gas forced-air furnace. It is a round-shaped switch that is fairly easy to identify once you have removed your furnace's front cover.
What does a flame sensor look like on a furnace?
The sensor is located just outside the burner assembly and looks like a small rod with porcelain surrounding the end that connects to the burner. Some furnace flame sensors are straight while others bend at a 45-degree or 90-degree angle.
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 high temperature limit switch?
The high-temperature limit switch is a small but important device used in forced-air furnaces powered by natural gas, LP, or heating oil. 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.
How to fix a bad limit switch?
A bad limit switch is usually handled by a furnace repair professional, but it can be replaced by a DIYer with a basic understanding of electrical issues and who understands how to use a multi-meter. The repair involves disconnecting and removing the switch, then checking it for continuity. If the multimeter shows that resistance is infinite, it means the switch is bad; replacement is a matter of simply inserting a new limit switch, attaching the mounting screws, then reconnecting the wires.
How does a limit switch work?
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. When the air in the plenum reaches the lower setting on the limit switch, the switch turns on and activates the blower fan, circulating air through the heat exchanger on its way to the house while simultaneously pulling cool air from the house through the air returns and into the furnace.
Why is the limit switch important?
The other important function of the limit switch is to shut off the burners if the heat exchanger gets too hot— a condition that can crack the piping in the exchanger, effectively ruining the furnace. Overheating can occur if there is a problem with the blower fan or if the furnace filter is so dirty that it restricts airflow through the furnace and exchanger so that the exchanger doesn't cool as it should.
Where is the probe on a furnace?
The probe extends through the wall of the furnace, and the plate fastens to the outside of the furnace's hot air supply plenum, above the combustion chamber or heat exchanger. The mounting plate usually contains two or more terminals that receive control wires for the blower fan and the furnace's gas valve.
Why won't my furnace run?
A bad switch also can prevent a furnace from operating at all. If the switch has completely failed and is stuck in the open circuit (off) position , the furnace won't run.
Why does my furnace limit switch trip?
With less airflow going through your furnace, the heat exchanger excessively heats up and causes the limit switch to trip .
Why use a high limit switch?
The high limit switch helps to protect the heat exchanger from getting cracked from excessive temperatures.
How to remove high limit switch from plenum?
Remove the high limit switch from the plenum by unscrewing it and taking out the wire connectors. Note: Do not touch the sensor. Hold it by the base instead. Oil from your fingers can create a hotspot that will cause the sensor to crack.
Why does my furnace trip out?
The high limit switch in a furnace can sometimes get dirty. When the limit switch is dirty, it will have trouble working properly, causing your furnace to trip out excessively.
Why does my furnace heat exchanger crack?
Prevents heat exchanger damage: Excessive temperatures in your furnace might cause the heat exchanger to crack .
How to clean a limit switch sensor?
Clean the limit switch sensor using fine-grit sandpaper or a scouring pad. Avoid steel wool since that will scratch the sensor surface.
What to do if you are not comfortable working on your furnace?
Note: If you’re not comfortable working on your furnace, then call an HVAC professional to check it out instead.
Where is the high limit 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.
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. But that’s not the only thing that the high limit switch does. It’s also safety device that helps prevent your furnace from overheating.
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 do blower fans need to be controlled?
The blower fan needs to be controlled by the limit switch rather than the thermostat . This is because you don’t actually want the blower fan to turn on and off at the same time as the gas burner. When the burner first comes on, it takes a while to heat up the heat exchanger.
What happens when the thermostat detects the air in your home has reached its set temperature?
Now, when your thermostat detects that the air in your home has reached its set temperature, the thermostat tells the gas burner in your furnace to turn off. But the blower fan keeps running for a little while.
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.
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 are furnace limit switches?
Furnace limit switches are electromechanical devices with momentary contact.
How does a limit switch work on a furnace?
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.
How to replace a high limit switch?
Most important, before attempting a replacement, make sure the switch actually is defective. Turn power off to the furnace (a must in any component replacement). Use an ohmmeter to measure resistance across the switch, which, if the temperature is below the setpoint, should be zero.
Why is my furnace overheating?
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 ...
Where is the limit switch on a furnace?
In most cases, the limit switch will be located inside the cover panel of your furnace. (You might need a screwdriver to remove this panel, depending on the model of your system.) On older furnaces, however, it may be set up on the outside of your furnace.
What is a furnace limit switch?
In basic terms, a furnace limit switch is a device within your furnace that detects when the internal temperature is too high and then brings it down to a safer level. You may also hear it referred to as a fan limit switch or a limit switch.
How do I know if my limit switch is bad?
As we’ve covered, your limit switch can signal other issues with your furnace that aren’t necessarily related to the switch itself. So how do you know if it’s your switch that’s the problem? Here are some warning signs.
How much does it cost to replace a furnace limit switch?
You can find new switches for less than $20 at your local hardware store. However, if replacing the switch doesn’t solve your issue, you should contact an HVAC expert.
What happens when the furnace is at a high temperature?
When the unit is at an appropriate temperature, the limit switch furnace will keep the burners activated and continue sending out heat. If the temperature gets too high, the switch will turn off the heat-producing burners and activate the blower fan to cool down the system.
Why does my furnace keep shutting off?
Does your furnace keep shutting off unexpectedly or running in shorter cycles? If so, you might have a problem with your furnace limit switch. Also known as a high limit switch, this small (but critical) component helps keep your home safe by automatically turning down the temperature when your furnace gets too hot. In this guide, we’ll explain how your furnace high limit switch works, how it impacts your home, and solutions for when it malfunctions.
What happens when a furnace switch is locked?
When your switch repeatedly trips, it may enter a “lockout mode,” where the furnace will completely shut down. This can only be reversed by servicing and resetting the furnace, which should be done by a professional.
What is a furnace fan limit switch?
Furnace fan limit switches also include a maximum temperature function that will disable the standard heating process if the furnace overheats. Lastly, the furnace fan limit switch may also be accompanied by a Manual On switch that allows you to keep the fan activated continuously throughout the day in your home to improve air flow.
Why is a furnace limit switch important?
The furnace limit switch is an essential component because it prevents your furnace from becoming too warm throughout standard operation. This is a safety feature that is designed to prevent damage to the internal components of your furnace and keep your family safe. In addition, the furnace fan limit switch is in charge if controlling ...
Why is my furnace deactivating?
If your furnace is continuously activating and deactivating throughout the day, this may also be a sign of a blower motor issue. An overheated blower assembly will trip the furnace limit switch and cause your furnace to deactivate prior to the end of the standard heating cycle. Other common issues that may affect the furnace fan limit switch ...
How does a furnace produce heat?
The burners are designed to heat the air produced by the air plenum in your furnace. Each burner works in conjunction with the furnace limit switch to ensure the air from the plenum is at least 20 degrees above the room temperature.
Does the furnace blower remain in session?
However, the blower assembly will remain in session until the furnace limit switch confirms the internal furnace temperature is at a safe level. Ways to Decrease Your Air Conditioning Bills.
Can a clogged furnace filter cause a furnace to overheat?
Lastly, we always recommend checking the filter in your furnace to confirm it isn’t clogged. A clogged air filter may cause the plenum in your furnace to reach an unsafe temperature. Once the plenum overheats, the furnace limit switch will turn off the furnace to keep you safe. To receive help with a furnace limit switch repair, ...
