Furnace Limit Switch – The Essential Guide

As a homeowner, you need to know that your furnace has a lot of vital components. One is the furnace limit switch or a high limit switch. It is a critical part of it. Having a faulty one could put your family in harm’s way. 

In this article, we’ll discuss furnace limit switches. We’ll also discuss what to do when it stops working. We’ll give insight into its regular maintenance for an optimum furnace. Let’s start. 

What Is a Furnace Limit Switch?

A furnace limit switch is a part of a forced air furnace. It is responsible for turning on the furnace blower once the desired heat has been attained. Without it, a furnace can’t regulate the temperature in conjunction with a thermostat. 

A furnace limit switch consists of an exterior plate and a temperature probe. The two reside inside the furnace housing. 

How Does a Furnace High Limit Switch Regulate Temperature?

When the heat is up, a signal is sent from the thermostat to the furnace. It then turns on the unit. Upon heating up, the furnace limit switch closes, connecting the circuit and turning on the blowers. 

Once the home or business comes to the desired temperature, the furnace burners will shut off. Yet, the blower will continue until the temperature inside the furnace decreases to the lower limit. 

Depending on the air temperature inside the home, the unit will cycle. It will restart or stay off for an extended period. The furnace limit switch helps to increase furnace efficiency. 

As the house cools, the thermostat will transfer a signal back to the furnace to kick on. It will initiate the cycle once more. 

Why Do You Need a Furnace Fan Limit Switch?

The furnace limit switch is an important component. It safeguards the furnace from becoming too warm throughout standard operation. It is a safety feature crafted to prevent damage to the interface components of your furnace. In addition, it is in charge of controlling the temperature throughout your house and cutting cold drafts. 

Signs of a Faulty Furnace Limit Switch

1. Difficulty starting 

If your furnace is having trouble starting up, it could be a sign that the limit switch is bad. 

2. Overheating 

A faulty limit may fail to signal the blower to begin and end at the right time. It is the culprit of the furnace overheating. 

3. Inconsistent operation 

One common issue also is if your furnace keeps going on and off. And it takes place throughout the day. 

4. Continuous fan operation 

When a high-limit switch goes bad, one of the most common dilemmas is failure to signal the blower fan to turn off. If your fan keeps running, it could be a sign. 

5. No heat production

If the high limit switch fails in its second function, it turns off the gas when there is no danger of overheating. Then, the furnace cuts in, producing heat. 

6. Inconsistent temperatures and strange noises 

The two are also common signs of a limit switch failure. 

Troubleshooting Steps for a Malfunctioning Limit Switch

1. Checking and resetting the limit switch 

One standard indicator of a faulty limit switch is when the furnace fails to turn on completely. Suppose you’re experiencing this dilemma. Checking and resetting the limit switch is critical. 

Before starting the process, ensure that the necessary safety precautions are taken. Turn off the power of the furnace. To reset the switch, find it near the main blower assembly. Press the reset button. 

If the furnace still doesn’t turn on, testing the switch for continuity may be critical. Use a multimeter for this one.

2. Cleaning and maintaining the limit switch 

Cleaning and maintaining the limit switch is vital, too. It can help prevent issues such as shutting off too soon and resisting turning on. 

To clean the limit switch, begin by turning off the furnace. Disconnect the power. Carefully remove the switch cover. Then, clean it with a soft brush or compressed air. Be sure to check for signs of damage and corrosion. 

Common causes of a malfunctioning limit switch include dirt buildup and clogged air filters. Thus, you can replace the air filter, too. Moreover, inspect if the fan motor has any obstructions.

3. Replacing a defective limit switch 

You’ll need to turn off the power to your furnace to replace a defective limit switch. Carefully remove the switch cover.  

There are several replacement options you can consider. If you’re confident in your DIY skills, you can grab a new one from a hardware store. You can install it yourself. If you’re uncomfortable with this task, seeking professional guidance is best. 

It is also best to check for any loose connections or damaged wiring. Sometimes, tightening a loose wire can fix the issue.

Importance of Regular Furnace Maintenance

1. Safety

The limit switch is a critical safety feature. It prevents the furnace from overheating. It turns off the burner when the temperature around the heat exchanger becomes too high. 

2. Efficiency 

The limit switch also plays a massive role in maintaining the heating system’s efficiency. It ensures the proper operation of the furnace blower. 

3. Reliability 

Cleaning and lubricating. These two maintenance acts can help prevent malfunctions. It can then lead to more reliable heat production. Also, there is less downtime. 

4. Longevity 

Taking good care of the limit switch can guarantee your furnace’s longevity and efficiency. It helps avoid premature wear and tear of this component.