What does the furnace limit switch do?

What Does a Limit Switch Do? The limit switch is a device that has two functions: first, it won’t allow the fan to turn on until the air generated inside your furnace is warm enough and second, it acts as a kill switch to the burner should the air temperature around the heat exchanger become too hot.

Likewise, what does a limit switch on a furnace look like?

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. If the temperature inside of the plenum gets too hot, it shuts off the gas supply to your burners to prevent your furnace and heat exchanger from overheating.

Also Know, where is the furnace limit switch located? The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner.

Likewise, people ask, can you bypass a limit switch on a furnace?

First, turn the power off to the furnace. If you have an ohmmeter, you can measure the resistance across the switch. If the temperature is below the setpoint, the resistance across the switch should be zero. If you do not have an electrical meter, you can temporarily bypass the switch and see if the furnace works.

What does it mean when the limit switch is open?

Limit switch codes If the furnace failure code indicates an “open limit” or “open high temperature switch” or “open rollout switch”, it is probable that the furnace has overheated. Limit switches turn off the burner and turn on the circulating fan if there is a high temperature condition in the furnace.

19 Related Question Answers Found

What causes a high limit switch to trip?

When you close registers, you restrict air flow which causes the plenum temp to get hotter. Furnaces require sensing airflow before they will enable the ignitor/gas valve. Additionally – just read that having gas pressure too high at the furnace will cause high limit trips.

How do you reset a limit switch?

How to Reset a Furnace Limit Switch 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.

What does open high limit mean on furnace?

In modern furnaces an open limit switch will always bring on the main blower as a safety feature when there is a call for heat but it is not the blower control which usually operates on a timer built in to t The limit switch will open periodically to prevent over heating.

How do I reset my furnace?

How to Find My Furnace Motor Reset Button Turn off the power to the furnace at the circuit breaker. The circuit breaker is clearly marked. Lift up the blower compartment cover to access the blower wheel and blower motor. Look for a small red or yellow button on the side of the blower motor. Press the reset button down if it has popped up.

How much does a high limit switch cost?

Another safety control is a high limit switch, which measures the temperature of the furnace to ensure it is running within safe temperatures. Both of these are small but critical parts for safe furnace operation, and they will run from $150 to $400 to repair.

What is a high limit switch?

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.

Where is the limit switch on a Rheem furnace?

Look for the fan limit switch, which is mounted to the side of the furnace plenum. Look for a flat, round component that is labeled “Fan Limit.”

What causes furnace to overheat?

A clogged air filter restricts airflow through the heat exchanger, causing the furnace to overheat. The high-limit switch detects the dangerous overheating and signals the computer to shut off the burners and run the blower fan to cool off the heat exchanger. Once the furnace cools, the computer tries to fire up again.

What is the switch on my furnace?

Beside or near your furnace will be a light switch, this controls the power to your furnace. Sometimes when your furnace does not respond to a request for heat from your thermostat, it is a power issue. First, check to make sure that the switch is in the “On” position.

What is a low limit switch?

The limit switch includes a sensor in the heat exchanger to determine when the air is warm enough to circulate. The switch also turns off the blower ff when the air temperature falls below a lower limit. As a safety measure, the limit switch shuts off the burner when the air in the system exceeds a maximum temperature.

What is a rollout switch?

The rollout switches are placed as a safety device around the burner area to sense the hot flame or hot exhaust thus shutting down the furnace so you do not get a fire or get carbon monoxide poisioning. The push button manual set rollout switch is located in the middle.

Do high limit switches go bad?

Like any other part in your HVAC system, the high limit switch can wear out over time. 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.

How do you reset the limit switch on a Lennox furnace?

Examine your furnace and look for a raised button or switch to the right of the ignition control box (or the “Limit Control” switch). Press and release the limit control switch to rest your Lennox furnace.

How does a limit switch work?

Limit switch. A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.

How do you reset a flame roll out switch?

Press and release the raised red button at the center of the flame roll-out switch to reset the furnace. You can press the reset button up to three times before troubleshooting the furnace’s internal components or calling for repair service; allow 30 minutes between each reset.

How do you adjust a fan limit switch?

How to Set a Fan Limit Control Switch Open up the access panel on the furnace. Look for the fan limit control switch encased in a small rectangular box. Slide the cover off the control switch or lift it up. Set the markers to the appropriate settings for your furnace. Pull out the white switch to reset the limit control to automatic.

Where is the plenum on a furnace?

A supply plenum is an enclosed compartment that’s located just after your heat exchanger if you follow the flow of air through your furnace (see below). When your air handler blows air over your system’s heat exchanger, that warm air is directed into the supply plenum.

How do electronic thermostats control cycling?

How do electronic thermostats control system cycling? A. These thermostats often use thermistors or other integrated circuit sensors to sense temperature changes. Thermistor operation is based on the fact that the electrical resistance of a ceramic semi-conductor changes as its temperature changes 7.

How do I know if my 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.

Leave a Comment