Timberline Blog
What Is a Furnace Limit Switch and Why Is It Important?
You may have heard the term “limit switch” regarding furnaces. It’s a vital component that affects the safe operation of your furnace. Consequently, if it begins to go bad, as all components eventually do, it’s important to recognize the signs and contact an HVAC company right away.
Understanding Your Furnace Limit Switch
You notice that your furnace is shutting down abruptly or operating in very short cycles. Initially, you may think this is just related to the temperature in your home or business, with your furnace bringing it up to the thermostat setting more quickly than usual for some reason. But this odd functioning continues.
What’s the cause? Your furnace limit switch likely is failing.
The limit switch—sometimes called a “high-limit switch,” which gives more of an indication of its function—protects your furnace and your home or business by automatically bringing the temperature of your furnace down if it gets too high.
Under normal conditions with a properly functioning limit switch, your furnace operates as follows:
- You turn up the heat on the thermostat.
- The furnace burners activate to start heating air in the plenum.
- When the air reaches the appropriate temperature, the system starts moving it through your ductwork to the vents.
- As this is happening, the limit switch monitors the temperature in the furnace.
- If the furnace gets too hot, the limit switch shuts down the burners and activates the blower fan to cool the system.
- When the furnace temperature is back in the normal operating range, the limit switch allows the burners to activate again.
This cycling occurs repeatedly throughout the day in the cool-weather months, with the limit switch playing that key oversight role.
Furnace Limit Switch and Safe Furnace Operation
Not only would allowing a furnace to get too hot potentially damage the equipment, but it also would pose a threat to people in the home or business. First, there would be the risk of fire. However, a damaged furnace could also allow dangerous carbon monoxide to escape.
That’s why the furnace limit switch is so important. It’s also why a furnace starts shutting down unexpectedly if the switch starts to fail. For safety reasons, heating systems are designed such that without a properly functioning limit switch, they will not operate.
Signs a Limit Switch Is Failing
What are the signs that a limit switch is failing? In addition to the furnace stopping abruptly or doing what’s called short cycling, there are two other signs to look for. First, if the furnace blowers don’t seem to shut off when they should, that’s an indicator. And second, if the air coming out of vents is cool rather than warm, that’s a sign, as well.
The good news is that those are indicators that the system is functioning as designed and protecting you. However, you’ll want to have an HVAC provider like Timberline Mechanical check out the system as soon as possible. Obviously, in the winter months, you need a furnace that is producing warm air safely and reliably.
Other Causes of Furnace Limit Switch Tripping
Besides the switch itself going bad, there are other reasons for its “tripping” or shutting the system down unexpectedly. For example, the limit switch gets information from a temperature sensor. If that sensor gets dirty, which sometimes happens, that can cause the limit switch to trip.
The switch can also trip as a result of airflow issues within the furnace. For instance, if your furnace filters are dirty, that can reduce airflow and cause the switch to trip.
Changing your furnace filter is something that you can and should do regularly. The schedule for changing filters will vary depending on the type of furnace and the filters used. Also depending on the type of furnace, you may be able to clean the temperature sensor yourself, but only if an HVAC expert has shown you how to do that.
When to Contact an HVAC Expert
The age-old wisdom, “Better safe than sorry,” certainly applies to HVAC systems in general and furnaces in particular. In this context, safety has multiple aspects. First, it’s vital that you have your furnace properly installed. If it’s not, the result can be a long list of ongoing or recurring problems.
Next, preventive maintenance is important. Some of those activities, like changing your furnace filters regularly, are steps you can take to ensure your furnace continues to function properly. However, getting periodic professional service is a good idea, too. An HVAC expert can clean and inspect your furnace, and in the process, spot any minor issues with your system before they become major problems.
Finally, if you ever notice that your furnace is operating differently for reasons you can’t explain—like a sudden, significant drop in the outside temperature that, understandably, will require your furnace to cycle on more frequently—it’s important to call an HVAC expert. First and foremost, they can address any safety issues with your system. But there are also cost savings to be considered.
For example, replacing or repairing a faulty system component before it has a negative impact on other components is much more cost-effective than having a major repair performed down the road. Plus, if your furnace is operating inefficiently, you probably are paying more to keep your home or business at a comfortable temperature.
A much better approach is to get to know Timberline Mechanical and the services we offer. Even if you don’t need one of our skilled HVAC technicians to perform a routine system inspection or perform preventative maintenance today, knowing you have a trusted provider who can perform those services or assist you if a furnace limit switch or other system component fails can be very reassuring.
The last position you want to be in is having your furnace fail in the cold-weather months, scrambling to provide an HVAC provider, and hoping the one you call has the expertise and attention to detail needed to solve the problem quickly and completely.
Contact Timberline Mechanical at your convenience.
Tags: furnace limit switch cost, furnace limit switch replacement, high limit switch, types of furnace limit switches
