Can You Bypass Furnace Limit Switch? [And Should You?]

You might have noticed that your furnace doesn't operate properly. And you might be wondering if the furnace limit switch can be bypassed in case there are issues. After examining numerous sources, we have come up with an answer.

Yes, you can bypass your furnace limit switch when testing, but you should not do so otherwise. Bypassing the furnace limit switch poses significant safety and fire risks, so if you must bypass it, you should seek the assistance of an HVAC technician to test it.

Below, we'll cover troubleshooting tips, alternatives, and solutions for your furnace limit switch. Each point is discussed in detail, so read on.

Man repairing a furnace, Can You Bypass Furnace Limit Switch? [And Should You?]

Bypassing the limit switch

Bypassing the limit switch is a common method for determining whether it needs to be replaced. However, while testing, the furnace should only be left open for a short period of time. Prolonged use of the furnace while testing poses significant safety and fire risks.

If you need to bypass your limit switch on your own, you can do so by following these steps:

  1. Switch off the furnace.
  2. Take off the furnace cover.
  3. Find the furnace limit switch. 
  4. Pluck the wires with pliers. 
  5. Connect the limit wires with a shielded wire. 
  6. Replace the furnace cover.
  7. Turn on the furnace.

A detailed guide is provided in the video below:

Safety and fire hazard

The furnace should not be left running for an extended period of time while testing the limit switch unless someone is watching it. This is due to the limit switch, which turns the furnace fan on and off as needed and shuts it down when it gets too hot.

The limit switch is a safety feature of a furnace that regulates its temperature and turns it off when it becomes too hot. Prolonged use during the troubleshooting may lead to overheating that may damage the heat exchanger which could eventually result in fires as well as the release of toxic fumes. These fumes can be inhaled by people in the household and may lead to health problems.

If you're unsure about the process, it is best to contact an HVAC technician to troubleshoot or perform the bypass for you.

Testing the limit switch

Technician repairing gas furnace

Limit switches in furnaces tend to be overlooked. In fact, many furnace owners don't know about them. A limit switch is an important safety feature. It regulates the air in the furnace and shuts it down when it reaches the specified temperature.

To avoid significant damage to the furnace and keep everyone in your household warm and safe, you should be aware of when the limit switch requires testing, repairing, cleaning, or replacing.

The following two indications should alert you to the fact that the furnace limit switch needs to be tested:

  1. The furnace fan doesn't stop running.
  2. The furnace fan is not running at all.

You might consider bringing out your tools and testing the limit switch once you notice any of these happening with your furnace.

Repair and Replacement

The best course of action for fixing the furnace is to replace the limit switch if testing reveals it to be faulty.

Use a multimeter set to the limit switch's lowest Ohms of resistance to test it. If there is no continuity, it means that it could be broken. A replacement is required if there is no continuity. However, even if there is continuity, the limit switch should be replaced if it causes the furnace to shut down too soon without even reaching the maximum  temperature specified.

Home repairman working on a furnace

A furnace limit switch replacement could cost between $5 and $20, depending on the equipment manufacturer. It is advised to purchase the replacement limit switch from the furnace's manufacturer. However, you can buy universal furnace limit switches if you want to go with a less expensive choice. A convenient option to purchase them is online. On Amazon, you can choose from a selection of limit switches.

You can purchase the furnace limit switch and replace it yourself, or you may seek professional help in replacing it. Expert labor fees differ depending on the problem and the parts in focus. In replacing furnace switches, labor costs from $150 to $300.

You can get service estimates from HomeAdvisor.

Can you run your furnace without a limit switch?

A home high energy efficient furnace in a basement

No, the furnace should not be used without a limit switch. Even with a bypassed limit switch,  the furnace should not be left open for an extended period of time. Limit switches control the furnace's temperature in line with the thermostat. Once the specified temperature is reached, the furnace fan is automatically turned off.

Without a limit switch, operating the furnace would require you to manually turn it off after the desired level of heat was reached. In any other case, there will be significant safety and fire risks brought on by the release of hazardous gases that can cause health problems, and overheating that can result in the eventual breakage of the furnace or even house fires.

How to prevent limit switch problems?

The key to avoiding furnace limit switch problems, particularly with older equipment, is routine maintenance and examination of the unit. Every time you inspect your device, you can easily do three things.

First, determine whether the sensor has to be cleaned. If it does, be sure to carefully wipe away any dirt, grime, or other debris that can prevent the limit switch from operating as it normally should.

The air filter should then be checked for clogging. The furnace plenum can become overheated and finally break due to a clogged air filter. The furnace plenum collects cooled or heated air from the furnace and sends it to the ducts so they can distribute it throughout your house. To avoid serious clogging, the filter should be cleaned once every two weeks.

Female hand sliding a new air filter into a furnace

Finally, check the air vents and ducts, making sure that they are open, free of blockage, and  are blowing air.

How to clean a furnace limit switch?

With long-term use of your furnace, it is unavoidable for it to collect dirt. Even limit switches for furnaces can become dirty, and if they do and they are not given proper care, difficulties with the furnace's general operation may result. Therefore, periodical cleaning of not only the unit but also the limit switch is advised.

While cleaning, be careful of touching the limit switch's sensor to prevent breakage. The sensor could develop a crack because of  the oil on your hands. Instead, you can use a scouring pad or fine-grit sandpaper to clean the limit switch while holding it by its base. Steel wool should never be used for cleaning because it can leave scratches in your sensor.

You can also have your furnace cleaned professionally. This is estimated to cost between $131 and $484. you may get a place-specific estimate of service costs by entering your zip code at HomeAdvisor.

How do you replace the limit switch by yourself?

Technician repairing furnace

While it is best to call contractors or HVAC technicians to check, troubleshoot and replace your furnace limit switch, you can still do it yourself. 

To change the limit switch on your own, follow these steps:

  1. Prepare the necessary tools for use (new furnace limit switch, screwdriver, and a multimeter)
  2. Turn off the furnace.
  3. Take off the furnace's cover.
  4. Replace the faulty limit switch.
  5. Test it with a multimeter to see if it needs cleaning or replacement.
  6. Replace the defective limit switch with a new one if cleaning is ineffective.
  7. Replace the furnace's cover.
  8. Switch the furnace on.

Check this video out if you need a more detailed guide to replacing your furnace limit switch.

In Closing

Although the furnace limit switch can be bypassed, doing so is not recommended. It should not be done for an extended period of time, except for testing purposes. Otherwise, there could be serious risks, like the release of toxic gases or overheating that could lead to a fire. Inhalation of these toxic gasses can result in serious health problems, and overheating may cause permanent damage to the furnace.

Instead, check the limit switch with a multimeter and then take the appropriate action to address the problem, such as cleaning or replacing it. You can clean and replace the parts yourself, or you can ask an HVAC specialist to assist you.

Check out these linked posts if you want more information on furnaces:

Furnace Not Kicking On – What Could Be Wrong?

No Power To Furnace – What To Do?

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