Can I replace my furnace's high limit switch with a comparable third-party part?


If you can find a suitable replacement part, surely you could replace a high limit switch yourself. However, if you don't know much about furnaces (or HVAC systems in general), you'll likely have a difficult go of it. If you're not experienced; and don't know anybody who is that could help you, it's best to contact a professional.

A high limit switch is designed to turn off the burner (heating element), if the temperature within the furnace is too high. In most furnaces when the limit switch opens (trips), the blower will continue to run to eliminate the excess heat. Most of the time the limit switch will reset, once the temperature has dropped enough. These devices tend to have a finite number of trips in them, before they stop resetting.

If the furnaces air filter is dirty, it can cause a restriction in the air flow through the furnace. If the air flow is reduced, not enough heat will be pulled away from the heater. The temperature within the heater will continue to...

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Video for Licensed HVAC Professionals ONLY, Please do NOT attempt any Procedures without Professional HVAC Training . (Hazardous) please click SHOW more link below

Service Call : (NO HEAT) determined High Limit Switch was going out do to Blower Motor going out .
Replaced Blower Motor & High Limit Switch !

Rochester Heating & Air Serves the Louisville Kentucky area including but not limited to:
Fern Creek , Middletown , J-town , St. Matthews , Valley Station , PRP , Shively , etc...

Hello ,
I'm Fritz Rochester , a Proud Kentucky Master HVAC Contractor , with over 20 years of experience in the Trade .
I would like to take care of all your HVAC needs . Whether it be a Service Call to get your HVAC System Up and Running Again , or a New HVAC Installation .
Rochester Heating and Air Strives to be one of the Best HVAC Companies in Kentucky .

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Once you've found the correct replacement, replacing the limit switch is quite easy really.

First, be sure you've shut of the power to the furnace either with the furnace service switch or at the breaker. These are the best ways to insure the power to the unit is off.

Now that the power is off, you simply remove the old limit switch and wire the new one back on the exact same way. With the new switches, this is even easier because there are likely only 2 wires coming off of the switch and 2 screws holding it in place. These 2 wires will also likely be held on by spade terminals which are very easy to work with.

The older limit switches are a bit trickier because there will probably be more than 2 screws holding it in, 3 wires to reconnect and there may also be a tab on the switch that you will have to read your installation instructions to determine whether it is to be snapped off or not. Be sure to look at your old one to see if it was an option on it as well...

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First, check to make sure all the information for the new limit switch matches to the old switch. This includes model number, serial number, manufacturer and voltage ratings.

Next, turn off the furnace using either the breaker or the furnace service switch. Use both to be safe. Wait until it has completely powered off before proceeding with the replacement. Remove the doors to the furnace and locate the old limit switch. Remove it by taking out the holding screws and separating it from the attached wires.

Once the old switch is removed, attach the new limit switch to the wires. When the wires are held in place, put the limit switch in its designated location. Hold the new switch in place and fasten the screws into their designated holes. Close the doors to the furnace securely. Turn the power to the furnace back on and let it run for a minute as a test.

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Natural gas furnaces ignite the burner before the blower turns on so that the heat exchanger has an opportunity to warm up before the air starts moving, eliminating a cold draft from the vents. Older furnaces use a mechanical temperature sensitive device called the fan-limit switch to know when the exchanger is warmed up. Newer furnaces have a control board with a built in time delay. If the heat exchanger becomes too warm, such as when the blower motor does not start or the return air path is blocked, there is a risk of fire. When this happens, the limit switch opens and shuts off the flow of natural gas to the burners. Since you say you are getting a "code", I will assume you have a newer furnace with a control board. Either the control board has failed to energize the blower motor or something is preventing sufficient air from moving through the heat exchanger and a temperature sensitive device is opening. Check the filter first. If it is dirty, it may not...

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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.

Types Of High Limit Switches

When looking for a replacement, it's important to note that there are numerous limit switches used in many different applications. Users will find electromechanical...

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I see this problem many times during the heating season here in Louisville, KY. When your thermostat calls for heat the draft inducer (please see pictures below) should start which creates a draft in your vent pipe. If your vent piping is open and your pressure switch is working properly the pressure switch will close the connection between two wires and send a signal to the control board saying, “Yes it is OK to continue with the ignition process.”

Above are pictures of a draft inducers showing where the pressure switch tube attaches. Pressure switch tubes sometimes attach on the top bottom or near the center of the draft inducer. These are just two of hundreds of different draft inducer designs. Some are metal and some are plastic. Most of the time draft inducers are plastic on 92% furnaces & metal on 80% furnaces. Make sure the opening where the pressure switch tube is attached to the draft inducer is open. Sometimes a small wire can be used to reestablish...

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There are two kinds of limit switches.

The first that we will try to locate is the Main Limit Switch so we can bypass it.

It is a rectangular or square looking device that has two wires attached to it and is usually located inside the furnace cabinet and sits on the back panel wall just above the gas valve. Locate it and let me know when you find it.

It is usually about 2 inches X 3 inches.

i see the gas pipe coming in, and it comes to a circular silver looking thing that also has the on/off switch on it, is that it?

No that is the gas valve.

Look behind the gas valve on the back panel wall inside the furnace cabinet.

on the back panel there is a black plastic, about 2X3, thing with two wires coming out of it, but there doesn't seem to b3e any switches or anything on it

one red and one white wire if that helps any

does it have any writing on it?

yes, looks like a upc code and some other serial numbers and...

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Now that winter’s nearly here, it’s time for a pop quiz: You wake up in the morning and there’s ice on the dog’s water dish. What do you do?

If you had trouble with that one, it’s time for a quick lesson on furnace troubleshooting. Here are nine easy tasks you can perform yourself, before you call in a repairman, to try and get your gas furnace—the nation’s most popular type—to start kicking out the heat again.

Step 1: Make sure the thermostat is set to “Heat.”
“This sounds obvious, but it’s true: a lot of people don’t have their thermostat set right,” says Bobby Difulgentiz, director of product management for Lennox International. So the first step in troubleshooting your furnace is to double-check that the thermostat is set correctly. “Many thermostats have to be physically set to “Heat,” says Difulgentiz. That switch can easily get moved—say, during dusting. He also advises to make sure the set point is at a...

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1. MYTH: The bigger the air conditioner, the better it will cool my house.

BUSTED: Oversize units may create bursts of cold air, tricking thermostats or control systems into shutting off the system before the entire house reaches the desired temperature. This “cycling” may end up causing excess wear and tear on the unit, affecting your indoor comfort level, and influencing your overall energy costs.

When an air conditioner is sized and installed properly by a professional HVAC technician, it will cycle on and off at various intervals to maintain the temperature setting on the thermostat or control system. It is not unusual for an air conditioner to operate using long on and off cycles. In fact, this is preferred for energy efficient performance and humidity removal. When a unit is not properly sized and installed, the unit may cycle on and off quickly and quite frequently. This situation may not allow the unit to operate as efficiently as it was designed and...

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