Your Furnace And The Furnace Limit Switch

Posted on: 18 December 2018

Keeping your furnace in good working order is important, especially if you don't want to end up without heat in the middle of winter. Part of your routine maintenance responsibilities is regularly changing your furnace filters. If you don't tend to this task, your indoor air quality will be poor, which can make it tough for people with allergies, asthma, and respiratory disorders. Dirty filters will also make your furnace work harder than it needs to, which can lead to breakdowns and a bad furnace limit switch. Here's what you need to know if you find yourself in this situation.

What Does A Furnace Limit Switch Do?

A furnace isn't overly complicated, but many of its systems are safety mechanisms to protect both the furnace and you. A furnace limit switch is one of these safeguards. It is a part of the control system as well as the blower.

When you turn your furnace on, the burners are cold. They need time to heat up. The furnace limit switch temporarily prevents the air handler from kicking on. If it didn't, your blower would blow cold air around your house — the last thing you want when you need heat.

What Happens When A Furnace Limit Switch Stops Working?

The furnace limit switch also acts as a safety mechanism by shutting off the burners when the air around the heat exchanger gets too hot. When a heat exchanger becomes dangerously hot, it can crack. These cracks are internal and not easily detected. A cracked heat exchanger will lead to serious safety issues as the byproducts of combustion — carbon monoxide, carbon dioxide, nitrogen dioxide, and sulfur dioxide — are released into the air. Breathing in these dangerous gases can cause illness or even death.

A furnace limit switch usually stops working eventually because it isn't allowed to work efficiently. In order to work properly, it needs to have good airflow. If your furnace filter is dirty or clogged, the furnace limit switch isn't going to get the airflow it needs, and it is going to have to work harder to counteract this. Eventually, it will fail completely, taking away one of your primary safety mechanisms. Your blower will also never kick in, which means warm air won't circulate through your vents and home.

How Is A Broken Furnace Limit Switch Repaired?

Rather than repair a broken limit switch, it is generally safest to replace the part altogether. Keeping your filters clean can reduce the likelihood of needing a new one. If you suspect your furnace limit switch has stopped working, turn off the furnace and call an HVAC professional immediately.


Lowering Your HVAC Expenses

After we purchased our very first home, I realized that I was really struggling with paying for the heating and cooling costs. We were spending much, much more money every month than we thought we were going to, and it was really difficult to figure out what we should do. We thought long and hard about how to minimize our expenses, but we didn't really get anywhere until we talked with an HVAC contractor. He mentioned specific, actionable ways to lower our bill, such as programming our thermostat and using more of our ceiling fans. This blog is all about lowering your bill.

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