The Limit Switch Protects Your Furnace From Overheating, But The Switch Can Go Bad
Your furnace has a safety switch in it that helps keep you safe and protects the furnace at the same time. The limit switch turns the furnace off if it overheats. It also regulates the blower by turning it on and off at the right temperatures. When the limit switch goes bad, your furnace can't work properly. Here are signs your furnace might have a bad limit switch and the repairs that might be needed.
When To Suspect The Limit Switch Is Bad
If the blower on your furnace keeps running and won't shut down even when your house is the right temperature, the problem could be the limit switch. One job of the limit switch is to turn off the blower when the heating cycle is complete, and if the switch is bad, the blower just keeps on working.
When To Suspect The Limit Switch Is Triggered
It's important to differentiate between when the limit switch is bad and when it's doing its job. If your blower turns off too soon, the limit switch might be turning off the furnace because the furnace is overheating. This can be caused by a clogged filter or dirty blower. The limit switch can also shut down your furnace and keep it off if the combustion area gets too hot.
If this part of your furnace gets too hot, the pipes could crack and possibly leak carbon monoxide, so once the limit switch has turned off the furnace a few times, it eventually keeps it shut down until the problem has been corrected. A heating repair technician can measure the resistance in the switch with a meter to tell if the switch is bad or if something else is wrong with your furnace and causing the switch to trigger.
What Type Of Heating Repairs May Be Needed
If the limit switch shuts down your furnace because the furnace is overheating, the technician may need to clean dust and grime off the blower and motor or clean the ignition area. They may also change the filter and ensure the furnace has adequate airflow. If it turns out the limit switch is bad, then the technician will replace it. This involves removing the switch and disconnecting the wiring and replacing it with new parts. Once the new switch is installed, the technician will probably run it through a full heating cycle to verify it's working properly.
One thing you don't want to do is attempt to bypass the limit switch yourself. If your furnace isn't working because of the switch, repairs are essential or the furnace could overheat, crack the exchanger, and cause serious and expensive damage.