Why Does My Furnace's High Limit Switch Keep Tripping?

Has your furnace started shutting off suddenly? Maybe it’s struggling to keep your home warm.

Regardless, a non-working furnace can be a huge headache. Luckily, the culprit is usually pretty easy to suss out, as most cases have to do with a tripping high-limit switch. Though small, this component is one of the most important operational pieces of your furnace. This is because it protects it from overheating. 

This doesn’t do you any good if you’re a Pacific Northwesterner dealing with damp, chilly winters. 

If you want to address this issue now and prevent it in the future, come with us as we take a look at all you need to know. 

What Is a High Limit Switch?

The primary job of a high-limit switch is to monitor the internal temperature of your furnace. When your furnace gets too hot, the switch will shut it off to prevent damage and keep your home safe.

However, your high-limit switch also keeps your furnace running efficiently by making sure it’s never working harder than necessary to keep your home warm. 

4 Common Reasons a High Limit Switch Keeps Tripping

There are several reasons why your furnace’s high-limit switch may be continuously tripping. Although there are a few reasons we deal with more than others:

Restricted Airflow

If your furnace is unable to "breathe," it’ll likely overheat. When your system overheats, your high-limit switch has to trip to cool it down. 

More often than not, restricted airflow is the result of clogged air filters, blocked vents, and dirty ductwork. The moral of the story is to keep your system clean so that your furnace doesn’t have to work overtime to push warm air.

Overheating Furnace

Now, of course, if your high-limit switch is flicking on each time your furnace overheats, it’s just doing its job. Some of the main furnace overheating causes include:

• A malfunctioning blower motor: Your blower helps circulate warm air. If it’s not working, heat can build up inside the furnace.

• A dirty heat exchanger: When you get dirt or soot buildup in your system, it can reduce its ability to transfer heat effectively.

• Poor maintenance: Skipping routine maintenance is one of the primary reasons homeowners are left with inefficient furnaces. 

Faulty High Limit Switch

Sometimes, high-limit switches fail, especially if they’re worn out or defective.

This is usually most obvious if you’re dealing with frequent shutdowns, even when there’s no sign of overheating. We recommend having a professional come in to diagnose it, as they’ll be able to tell you if the switch needs replacement or if there’s something else plaguing your system.

Improper System Sizing

If your furnace isn’t the right size for your home, you likely deal with cycling issues.

A furnace that’s too big might heat your home too quickly, causing it to start and stop more often than it should. On the other hand, a unit that’s too small might struggle to heat your home at all, causing it to overheat.

Steps Homeowners Can Take

While some issues require professional help, there are a few things you can do right now to mitigate high-limit switch problems:

Check and Replace Your Filters

Pacific Northwesterner's are well aware of the moisture and allergens our air carries. This is one of the reasons it’s so important to replace your furnace filter regularly. 

So, how often should you replace a furnace filter? Most experts recommend swapping out your filter every 1-3 months. 

Inspect Vents and Registers

Make sure nothing is blocking your vents such as curtains or furniture, as it’s one of the main culrprits of furnace airflow problems. Your system requires proper airflow to run efficiently. 

Monitor Energy Bills and Performance

If your furnace is working harder than usual (you’ll likely know, based on constant overheating or higher energy bills than usual), it’s a sign something isn’t right. Address issues early on to prevent them from snowballing into larger, costlier ones. 

Why Professional Maintenance Is Key

Routine maintenance is the best way to keep your furnace running smoothly all year long. 

HVAC professionals are trained to diagnose and fix issues that might not be as obvious to the untrained, such as dirty heat exchangers, blocked ductwork, or bad blowers.

With regular tune-ups, you can keep your high-limit switch issues to a minimum and extend the life of your furnace overall.

How Much Power Does a Gas Furnace Use?

If you’re wondering how much power your gas furnace uses, it’s an important question for both energy efficiency and understanding your furnace’s overall performance.

While gas furnaces primarily rely on natural gas or propane to generate heat, they also use electricity to power essential components like the blower motor, ignition system, and control board.

How Many Amps Does a Gas Furnace Use?

The electrical components of a gas furnace typically draw between 7 to 15 amps, depending on the size and efficiency of your system. The exact amperage can vary based on factors like the model, age, and whether the furnace is running in heating or fan-only mode.

Electricity Consumption in Watts

In terms of electricity, most gas furnaces consume about 400 to 1,500 watts during operation. This includes powering the blower fan, which circulates warm air throughout your home. While the furnace’s primary energy source is gas, this additional power consumption is important to consider when calculating overall energy costs.

Energy Efficiency Tips

To minimize electricity usage and improve energy efficiency:

• Replace your furnace filters regularly to reduce strain on the blower motor.

• Consider upgrading to a high-efficiency furnace with modern energy-saving features.

• Schedule regular maintenance to ensure your furnace runs smoothly and avoids unnecessary power spikes.

By understanding how much power a gas furnace uses, you can make informed decisions about energy efficiency and potentially lower your utility bills, especially during the colder months in the Pacific Northwest.

When to Call a Professional HVAC Contractor

If you’re having a hard time troubleshooting your system’s issues on your own, it might be time to bring in the big guns. There are a few scenarios in which hiring a professional contractor is recommended:

• Continuous high-limit issues, even after changing the filter and checking the vents.

• Your furnace keeps shutting down.

• Your furnace can’t heat your home.

• You’re hearing strange noises from your furnace.

Final Thoughts: Don’t Ignore a Tripping High Limit Switch

While it might seem okay to ignore a high-limit switch tripping issue because you don’t want to spend the money on a repair right now, it could end up damaging other components of your system and forcing you to spend more money down the line on larger repairs and increased energy bills. Not to mention, it could put your home at risk for fire. 

Today is the day to start taking proactive steps and scheduling regular maintenance.

Whether you’re looking for quick and reliable high-limit switch repair or you just need regular HVAC system repair contact us today to schedule an inspection! We provide the top HVAC services in Vancouver, WA, Portland, OR, and the surrounding Pacific Northwest.