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Dowd Mechanical Heating & Air Conditioning Blog

Why Your Furnace’s Blower Won’t Stop Running

dog-in-wind

If you use a furnace to warm your house each winter, you’re familiar with the sound of the blower, the fan that turns on to move around the hot air through the house. The blower is also responsible for sending air through the furnace to receive heat and to cool down the heat exchanger in the furnace at the end of the heating cycle. This is why you’ll notice the blower continuing to run for a few minutes after the gas burners have shut off. 

You might run into an issue with your furnace where the blower constantly runs. It isn’t always sending around heat, but it’s always blowing air. We’ll take a look at what can cause this and whether you’ll need furnace repair in Levittown, PA.

The thermostat is set to “fan on”

Many modern thermostats have two settings for the fan: “fan auto” and “fan on.” The standard setting is “auto,” which means the fan will automatically come on when the furnace begins its heating cycle and shut off at the end. (This also applies to the air conditioning system if they’re run from the same thermostat.) When the fan is set to “on,” it will run on its own until turned back to “auto.” Check to see if you’ve mistakenly turned the fan to “on” rather than “auto.” (Some thermostats have an additional setting, “fan circ,” where the fan turns on and off periodically to help with air circulation.) 

Bad thermostat connection

The thermostat has separate wires to signal to the fan to turn on and off. If the “off” wire shorts out, the thermostat won’t be able to send a signal to shut the blower off when you turn the thermostat to “fan auto” mode from “fan on” mode. 

A stuck motor relay

This is a common mechanical problem with motors that can lead to the fan running without stop. The relay on the blower motor opens to stop the flow of voltage and shut the fan off. The relay can become stuck, which will continue to allow voltage flow to the fan, even if it’s supposed to turn off. Technicians can fix this before the motor suffers serious damage from overheating. 

Faulty limit switch

The limit switch is a device that helps regulate the blower fan and the furnace burners. It senses the temperature in the furnace and activates the blower fan when it’s warm enough to start sending air through it. It later shuts the blower fan off when it senses the furnace has cooled down, and it can shut off the furnace in case of overheating. A faulty limit switch can cause the fan to run continuously (or not to run at all). The switch may also be incorrectly set to a manual override mode.

Control board problems

The control board is the central electrical switching station for the furnace that controls the various parts. Malfunctions in the control board can cause non-stop fan operation. You’ll always want experienced technicians to examine the board to see what’s wrong. 

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