If your furnace fan is running nonstop, it can be both frustrating and concerning. This issue not only leads to higher energy bills but can also indicate underlying problems with your HVAC system. In this blog post, we’ll explore some common causes of a continuously running furnace fan and how to troubleshoot them.
1. Check Your Thermostat Fan Setting
The first and easiest place to check is your thermostat. Most thermostats have three fan settings: Auto, On, and sometimes Circulate.
Here’s what they mean:
Auto: The fan will only run when the furnace is actively heating or cooling.
On: The fan runs continuously, regardless of whether the furnace is heating or cooling.
Circulate: The fan will run intermittently to circulate air, even when the system isn’t heating or cooling.
If your fan is set to “On,” it will run nonstop. Switch it to “Auto” and see if that resolves the issue. If the fan continues to run while the thermostat is correctly set to “Auto,” the problem may lie elsewhere.
READ MORE: Pros and Cons of Auto vs On Thermostat Setting
2. Inspect the Fan Limit Switch
If your thermostat settings are correct and your fan still won’t turn off, the next likely culprit is the fan limit switch inside your furnace. This switch is responsible for turning the fan on and off at the appropriate times.
Locating the Fan Limit Switch
To locate the fan limit switch:
- Turn off power to the furnace for safety.
- Open the furnace access panel.
- Look for a small, rectangular device mounted near the blower motor with a metal or plastic cover. It often has wires connected to it and a dial or probe extending into the furnace.
Potential Issues with the Fan Limit Switch
Manual Override: Some fan limit switches have a manual override setting. If the override is engaged, the fan will run continuously. Ensure the switch is set to “Auto” or its equivalent.
Faulty Sensor: The switch might be malfunctioning and incorrectly signaling the fan to run. This can happen due to wear and tear or a buildup of dirt and debris.
Stuck Switch: The mechanical components of the switch could become stuck in the “On” position.
If the fan limit switch is dirty, you may be able to clean it carefully. However, if it’s faulty, replacement is often the best solution. It’s wise to consult a professional for this repair.
3.Thermostat Wiring Issues
If the fan limit switch appears to be functioning correctly and set properly, the issue could stem from your thermostat wiring. Faulty or loose wiring can send continuous signals to the furnace fan to run.
Signs of Wiring Issues
- Your thermostat settings don’t seem to affect the fan’s behavior.
- The fan starts and stops sporadically or inconsistently.
An easy way to check to see if the thermostat is truly the issue is to remove it from the wall and see if the furnace fan still runs. If it is still going then the issue is within the furnace itself.
If the fan stops running when the thermostat is no longer connected then you’ll need to inspect the thermostat wires for signs of wear, corrosion, or improper connections. If you’re not comfortable handling electrical components, it’s best to call a licensed HVAC technician to diagnose and resolve the problem.
When to Call a HVAC Professional
While some troubleshooting steps can be handled by homeowners, more complex issues like replacing a fan limit switch or addressing wiring problems are best left to professionals. At Quality Comfort Home Services, we specialize in diagnosing and repairing HVAC issues, ensuring your home stays comfortable year-round.
If your furnace fan won’t turn off, give us a call today. We’re here to help families in Cincinnati get back to enjoying a warm, energy-efficient home.
