Why is my furnace fan constantly running?

Why is my furnace fan constantly running?

When your thermostat is set to AUTO, your furnace fan should blow only when your furnace is in the middle of a heating cycle. But if your fan runs constantly, regardless of whether your furnace is heating, that’s not normal. There’s a shorted thermostat wire. There’s a shorted wire at the fan limit switch.

Why wont my furnace fan shut off?

If your furnace fan won’t turn off, you most likely have one of these 3 problems: Your furnace fan limit switch is set to “manual override” The fan limit switch is faulty and needs to be replaced. There’s a problem in your thermostat wiring.

Does the furnace fan continue to run if the high limit switch opens the furnace control circuit?

The furnace burner and the blower fan will continue to run (usually) as long as the thermostat is calling for heat, so warm air is continually delivered into the occupied space. The thermostat stops calling for heat.

How do I know if my high limit switch is bad?

Check Your Limit Switch “If the high limit switch was bad, the furnace should not fire. When the high limit switch trips, the flame/heating element will be shut off and the blower will continue to run to clear the heat. The blower will continue to run until either the system is reset, or the limit switch closes.”

How much does it cost to replace a high limit switch?

Another safety control is a high limit switch, which measures the temperature of the furnace to ensure it is running within safe temperatures. Both of these are small but critical parts for safe furnace operation, and they will run from $150 to $400 to repair.

Why does my furnace high limit switch keep tripping?

If the air inside your furnace gets too hot, the limit switch trips to prevent overheating. If the furnace high limit switch trips due to overheating, there is likely an airflow issue that is preventing proper air movement through the system. A dirty filter is the most common cause of airflow issues.

Where is the high limit switch on my furnace?

The high limit switch is usually attached to a metal plate, which is bolted to the outside of the furnace plenum (the large metal box where air is heated.) You will have to remove the furnace cover to find it.

How does a furnace high limit switch work?

Also known as the fan limit switch or simply the limit switch, it has two functions in the furnace’s operation: It turns the fan on and off during the normal heating cycles of the furnace, and it senses heat and shuts down the furnace if the interior temperature gets too high.

How do you test a furnace fan limit switch?

Watch the oil or gas burner: The furnace oil or gas burner should turn ON and subsequently the FAN LIMIT control should turn the burner back OFF when the temperature in the supply air plenum reaches the FAN LIMIT set point. Watch the dial on the fan limit switch moving to confirm its operation.

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