Furnace Error Code Limit Switch Open: 8 Things You Can Check to Fix This Problem

Furnace Limit switch error codes are a frustrating part of operating a gas or oil furnace. They can happen at the most inconvenient times, such as when you’re cold and want to turn up the heat. Or when it’s the dead of night and you have to get up for work in a few hours. Then again, maybe it’s just perfect timing and you can get that repair scheduled before your next business trip or vacation. Limit switch error codes are frustrating no matter what time of day they occur. The good news is that there are many potential solutions to fix a furnace limit switch error code. You might even be able to do them all from home with simple tools that you probably have lying around somewhere in your house. Let’s take a look at everything you need to know about fixing this problem with your furnace, including the 8 things that cause this issue:

What is a Furnace Limit Switch Error Code?

A furnace limit switch error code is a furnace error code that is triggered when the furnace tries to start up and the limit switch detects either a short-cycle or a fault condition within the system. The limit switch is meant to protect the rest of the furnace components from damage in the event of a short cycle. The limit switch is usually a small, black box that sits near the furnace blower. It’s wired to the furnace control board, and it has one job: turn the furnace off as soon as it detects a fault condition. Furnace Limit switch error codes will display a number on the furnace control board. This number is different for each furnace manufacturer, but it will usually be a number between 1 and 8. For example, a Limit Switch Open error on a Trane furnace will be displayed as “1-L-O”.

8 Things That Cause a Furnace Limit Switch Error Code

A furnace limit switch error code is caused by a variety of problems within the furnace system. Here are the 8 leading causes of a furnace limit switch error code: – Loose wiring- Dirty contacts- Faulty limit switch- Internal short-cycle- Faulty gas valve- Blocked condenser fan- Blocked dryer vent Let’s take a closer look at each of these potential causes: – Loose wiring- A loose wire might cause the furnace to trip the limit switch, but it won’t be consistent. This will cause the furnace to trip at random times, and you’ll never get the same error code twice. If you have a loose wire, it will trip the limit switch on and off, but it won’t cause a consistent error code like a Limit Switch Open. – Dirty contacts- Dirt and dust can build up on the contacts inside the limit switch box. When the contacts get dirty, they may not close all the way when the furnace shuts off. This will cause the furnace to trip the limit switch as soon as it tries to start up. You’ll get the same error code every time you try to start the furnace. – Faulty limit switch- If the limit switch is broken or broken, it will trip the furnace every time you try to start it up. You’ll get the same error code each time. If the limit switch is broken, it will probably trip the circuit breaker at the same time. – Internal short-cycle- An internal short-cycle happens when there is insufficient heat in the furnace. No matter how high you set the thermostat, the furnace won’t produce enough heat to satisfy the thermostat. This will trip the limit switch every time you try to start the furnace. You’ll get the same error code every single time. – Faulty gas valve- A faulty gas valve will not allow the furnace to ignite the burner. If this happens, the furnace will trip the limit switch immediately. This will cause the same error code every time you try to start the furnace. – Blocked condenser fan- The condenser fan pulls air through the furnace and pushes it into the outside air. If the condenser fan is blocked, the furnace will overheat and trip the limit switch as soon as it starts. This will cause the same error code every time you try to start the furnace. – Blocked dryer vent- The dryer vent runs from the outside of the house to the inside of the house, and then down to the outside of the house again. The vent must remain clear of blockages at all times. If you leave lint in the vent, it will accumulate and eventually cause the furnace to trip the limit switch. This will cause the same error code every time you try to start the furnace.

Check the Timing of the Problem

The first thing you should do when troubleshooting a furnace limit switch error code is to check the timing of the problem. When did it start happening? How often does it happen? How long does the problem last? You have to ask yourself these questions because many furnace issues are intermittent. They don’t happen all the time, and their timing can vary from day to day. There might be a loose wire in the furnace that trips the limit switch every time you try to start the furnace, but it might not trip every day.

Check the Gas Valve

The gas valve is the device that regulates the amount of gas used to ignite the furnace burner. If there is a problem with the gas valve, it will cause the furnace to trip the limit switch immediately. This problem is easy to diagnose because you only have one gas valve to check. It’s also easy to fix because you can replace the gas valve with a new one from home. You have to exercise care when handling the gas valve, though. Don’t turn the burner screw off, otherwise, you’ll shut off the gas to the entire house.

Check the Limit Switch Itself

If you’ve ruled out all of the other potential causes of a furnace limit switch error code, you should check the limit switch itself. The good news is that you can easily open the limit switch box and take a look inside. This will allow you to check the contacts and wires for any signs of damage. If you find that the contacts are dirty, clean them off with rubbing alcohol. If there are signs of burn marks or other damage, you’ll have to replace the limit switch entirely. Replacing the limit switch can be done with common tools, but you’ll probably want to hire a professional to do the job for you.

Check the Dryer and Condenser Coils

The condenser fan pulls air through the dryer and furnace during operation. If the dryer and furnace coils are clogged or blocked, the furnace will overheat and trip the limit switch as soon as it starts. This will cause the same error code every time you try to start the furnace. You can diagnose this problem by opening the dryer and checking the coils for lint build-up. If the coils are clear, check the condenser fan and coils at the back of the furnace. If the coils are clean, you should hire a professional to clean them. You can’t do this job from home because you’ll need a special tool to remove them.

Reset the Furnace and Run Self-Diagnostics

When you can’t find the source of a furnace limit switch error code, the next thing you should try is resetting the furnace and running the self-diagnostics. You can do this by following these steps: This will reset any error codes in the furnace memory, which might help you identify the problem. You’ll probably see a Limit Switch Open error code show up again, though.

Replace the Gas Valve, Dryer, and Condenser Coils

If you’ve ruled out everything else, you’ll probably have to replace the gas valve, dryer, and condenser coils. Replacing these components can affect your furnace warranty, so you’ll want to call in a professional. These components are buried inside the furnace, and they’re not cheap. You can expect to pay anywhere from several hundred dollars to over a thousand dollars to replace them. This is the last resort when troubleshooting a furnace limit switch error code, but it’s not uncommon.

Conclusion

A furnace limit switch error code is frustrating, but there are