It’s one of the most common problems homeowners face with their HVAC systems. As an HVAC repair company with over 30 years of experience, furnace fan issues are among the most common HVAC repair calls we get in the winter. If your furnace fan runs continuously, it may be caused by a few different factors. This article will explain why your furnace fan keeps running, what the causes are, and how to fix them.
Quick Answer: Why Is My Furnace Fan Running Constantly?
If you’re searching “why is my furnace fan running constantly”, the usual causes are the thermostat fan setting being on, a circulation schedule, a fan limit switch set to manual, or a control board or wiring issue. Start by setting the fan to Auto, then power-cycle the system. If it still runs, call a pro.
Safety First
Before you troubleshoot:
- Turn off power to the furnace at the thermostat and the breaker if you will open panels or inspect internal components.
- Keep hands away from moving parts and sharp metal edges inside the cabinet.
- If you smell gas, feel dizzy, or suspect carbon monoxide, stop immediately and call a professional. Leave the home if you believe there’s an immediate safety risk.
Troubleshooting Flow: Furnace Fan Keeps Running
Use this quick flow to pinpoint the most likely cause before you dig deeper.
1. The Furnace Blower is Set “On”
The most common cause of a furnace fan running continuously is that the blower setting on your thermostat is set to “on.” This means that the fan will run constantly as long as there’s electric power. This will happen regardless of whether or not your furnace is actually heating. To fix this issue, you’ll need to change the settings on your thermostat. Just switch the fan setting to “auto” instead of “on.” This tells the system to only run the fan when the furnace is actually heating.
2. The Thermostat is Automatically Turning the Fan On and Off
Another possible cause of your furnace fan running continuously is that the thermostat itself is automatically turning the fan on and off. This can happen if you have an automatic timer set for when the system should turn itself on or off. Sometimes, it’s a smart thermostat that’s designed to turn on every hour or so to keep air circulating throughout the house. If this is happening, then you’ll need to adjust the thermostat settings so that it only turns on and off when necessary.
Contact Us to Fix Your Furnace in South Carolina
We have more tips on furnace fans below this form, but if you’re in need of furnace repair in South Carolina, feel free to fill out this form or go ahead and give us a call at 843-242-7065 to schedule your service.
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3. The Fan Limit Switch is in Manual Override Mode
In older HVAC units, the fan limit switch may be set to manual override mode. This means that the fan will run constantly until you manually turn it off. If this is the case, then you’ll need to find the fan limit switch and move it back into automatic mode. This will ensure that your furnace fan runs only when necessary and not continuously. The fan limit switch is typically located near the blower motor or in the control box. It just requires a press from your finger to behave accordingly.
Most homeowners find older HVAC units complicated to handle and they prefer to call in an HVAC technician for a repair or replacement when something isn’t working correctly. Before you do that, however, it’s important to check the most basic settings so that you can potentially fix the problem yourself. In this case, it may be as simple as adjusting the fan limit switch or changing the thermostat settings. That being said, if you’re not confident in your ability to diagnose or fix the problem on your own, it’s best to call a professional. They can inspect and repair the furnace quickly to ensure that your home stays warm and comfortable.
4. A Bad Thermostat
A faulty thermostat can cause your furnace fan to run constantly. Your thermostat should be checked for proper calibration, battery condition, and settings to ensure that it is working correctly. If you suspect an issue with the thermostat, try replacing the batteries or checking the wiring connections. You may also want to check the temperature settings on the thermostat. If you are still experiencing issues with your furnace fan running, then it is time to call in a professional for service.
5. A Bad Circuit Board or Shorted Wire
The circuit board or wiring in your furnace may be faulty, causing the fan to run continuously. This is a complicated problem that requires professional furnace repair. It is important to note that you should never attempt to repair these issues yourself as they can be dangerous and could reduce the longevity of your furnace system. A qualified HVAC specialist should be called in to diagnose and repair the issue.
Inducer or Exhaust Fan Runs Continuously
Sometimes homeowners say “the furnace fan won’t stop,” but the sound they’re hearing is actually the inducer or exhaust fan, not the indoor blower. The inducer is usually a smaller fan near the furnace venting that helps move combustion gases out safely.
If an inducer or exhaust fan runs continuously, common causes include:
- A control board or relay issue
- A pressure switch problem or venting restriction
- A safety-related condition keeping the system from completing a normal cycle
Because this involves combustion and venting, it’s best to stop troubleshooting and call a professional if you suspect the inducer is the fan that won’t shut off.
When to Call a Pro
Call a professional right away if:
- You suspect wiring problems, a short, or a damaged control board.
- Your thermostat appears fine, but the fan still runs nonstop.
- You suspect power issues or the furnace is not responding to thermostat changes.
- You see a damaged baseplate, loose low-voltage wires, or signs of overheating.
Contact Carney & Son 72 Degrees For Furnace Fan Repairs
If you are still having trouble with your furnace fan running continuously, it may be time to call in a professional for repairs. Our experienced technicians can diagnose the issue and repair it quickly so you can keep your home warm and comfortable. Schedule service today through our Heating Repair & Maintenance page or learn more about our full Furnace Services.
