What Does a Furnace Limit Switch Do?
The furnace that keeps your home warm on chilly nights has a crucial part called a fan limit switch. This piece signals the blower assembly when to power on and blow warm air up your ducts and throughout your home. The furnace limit switch, or high limit switch, also determines when the blower assembly should turn off—whether that’s due to overheating or your home reaching a warmer temperature.
What Does a Furnace Fan Limit Switch Look Like?
While it can differ slightly from one furnace manufacturer to the next, you can find the high limit switch by removing the furnace cabinet cover. The fan limit switch sits on a mounting plate and has a long temperature sensor that extends into the furnace plenum: an air chamber that fills with air from the blower fan. The plate has a wire that runs to the blower and one that goes to the gas valve.
How a Furnace Fan Limit Switch Operates
When your furnace thermostat notices your household temperature is too low, the burners are signaled to ignite and begin heating the air in the plenum. When the plenum air is hot enough, the fan limit switch tells the blower assembly to blow the heated air past the heat exchanger. This warm air should circulate into every room of the house using the air duct system. When the thermostat recognizes your home is sufficiently heated, it shuts off the furnace. The blower will keep running until the internal furnace temperature is low enough to stop.
If your furnace burner were to keep running even if the system itself were to work improperly or break then the high limit switch would shut off the gas valve to prevent a fire or similar danger.
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How Do I Replace a Furnace Fan Limit Switch?
Follow these steps to replace your broken or worn out furnace limit switch and save yourself from paying other local contractors several hundred dollars.
1. Furnace Deactivation
Turn off your furnace power using the service switch or your circuit breaker. This will prevent any safety accidents from occurring during the DIY replacement.
2. Removal & Configuration
After switching off the furnace, open up the furnace cabinet door and remove the old high limit switch. Place in the new switch by wiring it exactly like its predecessor. This usually only involves two screws, wires, and terminals. Follow its instructions so dial settings are the same as before or adjusted as needed.
If the model looks older: read the installation instructions if you need help following the small additional steps, such as wiring a third line, snapping on a tab switch, and adjusting dial settings to read the same as before. Otherwise, you can always call Fenwick Home Services to be sure it’s done right.
3. Operational Testing
After you’ve configured the new furnace limit switch, turn on the furnace and adjust the thermostat so that it signals the start of the heating process. Verify that your vent is blowing out a sufficient amount of warm air and that nothing seems out of the ordinary to confirm your successful switch replacement.
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How to Find a New Furnace Fan Limit Switch
Before you even begin to replace your furnace fan limit switch on your own, you may need help purchasing the part itself. Start by copying down your furnace model number, serial number, voltage/amperage ratings, and any other information you find necessary off the furnace and switch rating plates. Getting the operational temperature range and the length of the switch’s temperature sensor rod would also be worthwhile.
We suggest contacting a local supplier or dealer over trying a wholesaler, as they may be more equipped to support you and answer your questions as a homeowner. Shopping online can also smooth the process of finding the right high limit switch—just be sure all the specifications in the product descriptions match up with your existing piece.
If you’re worried about spending too much, damaging your furnace with the wrong piece, or just creating a headache: our technicians at Fenwick Home Services are more than happy to assist you with ordering and replacing your furnace limit switch for you. Trust our professionals to do it all perfectly.
Average Cost of a New Furnace Limit Switch
You will need to buy a high limit switch that is produced by the same manufacturer as your furnace unit. Depending on who your OEM is, this component could roughly cost you anywhere from $4 to $25. You might also find a universal switch on the lower end of this cost range, but we would advise you to consult your furnace manufacturer or a Fenwick serviceman to determine whether or not it would work in your model.
Furnace Repair & Replacement Services
If you believe you need a new furnace fan limit switch, call our team of licensed contractors by phone at (904) 217-5694 to schedule an appointment with a specialist to quickly resolve the issue. Our staff of technicians offers various types of HVAC services such as furnace repair, air conditioning installation, and heat pump maintenance. Our affordable, high-quality furnace repair and replacement services will optimize your heating system and maximize your energy efficiency. Get in touch with one of our certified, licensed team members today. Let’s keep your family’s home warm and cozy all winter long!
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