Why Does My Furnace Fan Run Constantly?

If you find yourself asking, “Why does my furnace fan run constantly?” you’re not alone. Many homeowners experience this issue, and it can be both frustrating and concerning. But fret not, as there are several potential reasons why your furnace fan might be running continuously, and understanding these causes can help you address the issue effectively.

1. Thermostat Fan Setting

One possible explanation for your furnace fan running constantly is the thermostat fan setting. Some thermostats offer a “fan” mode that allows you to manually control the fan’s operation independent of the heating or cooling system. If this setting is accidentally switched to “on” instead of “auto,” the fan will continue to run even when the heating or cooling cycle is not active.

To address this, check your thermostat’s settings and ensure that the fan mode is set to “auto.” This will allow the fan to run only during the heating or cooling cycles, as intended.

2. Fan Limit Switch Issue

The fan limit switch is a crucial component in your furnace that regulates the fan’s operation based on the temperature inside the furnace. If this switch malfunctions, it can cause the fan to run constantly. The switch may be faulty or incorrectly calibrated, leading to this continuous operation.

To diagnose this issue, you can visually inspect the fan limit switch and look for signs of damage or wear. However, it’s recommended to have a professional HVAC technician inspect and potentially replace the switch if necessary.

3. Blower Motor Problem

Another reason for your furnace fan running continuously could be an issue with the blower motor. The motor may be defective, causing it to run non-stop. Insufficient lubrication or a faulty motor control board can contribute to this problem as well.

If you suspect a blower motor problem, it’s best to enlist the help of an HVAC technician. They can diagnose the issue accurately and determine whether repair or replacement is necessary.

4. Blocked or Dirty Air Filters

Blocked or dirty air filters can also result in a continuously running furnace fan. When the air filters are clogged with dust, dirt, or debris, the restricted airflow can cause the fan to keep running in an attempt to compensate for the reduced airflow.

To remedy this, check your air filters regularly and change them according to the manufacturer’s instructions or as needed. By keeping your filters clean, you ensure proper airflow and prevent unnecessary strain on the fan.

5. Faulty Relay Switch

A malfunctioning relay switch can also be the culprit behind your furnace fan running constantly. The relay switch controls the fan’s operation by sending an electrical signal. If this switch gets stuck in the “on” position or fails to send the correct signal, the fan may continue to run continuously.

To resolve this issue, it’s best to consult a professional HVAC technician who can test and replace the faulty relay switch if necessary.

In conclusion, a constantly running furnace fan can be caused by various factors, including thermostat settings, a faulty fan limit switch, a blower motor problem, blocked or dirty air filters, or a faulty relay switch. While some issues can be resolved through DIY measures such as checking thermostat settings and changing air filters, it’s always wise to seek professional assistance for more complex problems. Remember, regular maintenance and prompt repairs can help keep your furnace fan running efficiently and your home comfortable.