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Carolina Climate Control Blog

Reasons Your Furnace May Be Shutting Down Early


When you turn on your furnace for the winter, you want it to heat your home so everyone is comfortable. In order for a furnace to do that, it has to run long enough to distribute heated air through the ventilation system to all the rooms.

But you’ve run into a problem: your furnace is shutting down too early, and the house isn’t getting the warmth your family needs. What’s happening? And what can you do about it?

You’ve come to the right place for answers!

The Furnace Heating Cycle

Before we go into the possible causes for your furnace turning off too soon, we want to talk about the heating cycle your furnace goes through. 

The heating cycle begins when the thermostat sends a request for heat to the furnace. The furnace control panel then opens the gas flow to the burners and ignites them. When a device called the limit switch determines the heat exchanger is hot enough, it turns on the blower fan to send air around the heat exchanger and then into the home. When the thermostat registers the target temperature has been reached, it signals the furnace to cycle down, starting with shutting off the burners. When the limit switch detects the heat exchanger has cooled down, it then shuts off the blower. This is the complete heating cycle.

Now, what can go wrong that will cause this cycle to stop far too early?

It could be the thermostat

If the thermostat isn’t reading the right temperatures in the house, it may instruct the furnace to shut off prematurely. A miscalibration of a few degrees can mean the thermostat thinks your house is warmer than it is, and you won’t be able to get to your desired temperature.

Maybe it’s a clogged filter

A dirty furnace filter left in place will restrict the heat flow into the furnace, and this makes it harder for the blower to send air around the heat exchanger. The heat exchanger will overheat, and that limit switch will activate to shut down the furnace for safety. 

The limit switch itself might be faulty

The limit switch can malfunction, just like any other component, and this will throw off the calibration between the blower and the burners. The limit switch may mistakenly think the heat exchanger has cooled down enough and shut the system off early, or it may think the heat exchanger is overheating and shut down the furnace as a safety precaution.

It’s possible the burners are dirty

If the burners are dirty, they won’t be able to draw enough oxygen to stay lit for long. If the burners shut off, a device called the flame sensor will cause the entire furnace to shut down.

Or maybe your furnace is just too old

If your furnace is more than 15 years old, shutting down like this often indicates the system is simply too worn from age to work correctly. 

So What Do I Do?

Check the filter first and change it to see if this fixes the issue. If it doesn’t, then it’s time to call us for furnace repair in Charleston, SC. Shut the furnace off at the furnace switch first, then get in touch with us. We’ll find out the problem and have it fixed ASAP.

Rely on Carolina Climate Control and we’ll say “The Moose Is Loose in Your Neighborhood!”

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