For the most part, furnaces will work without a hitch if annual maintenance is performed. However, a furnace system can sometimes be prone to improper wiring, a buildup of debris, and other issues that block air from blowing through the vents.
A furnace won’t blow air through vents due to clogged or dirty air filters, a circuit breaker that’s been shut off, broken blower motor, or faulty fan limit switch. To get the air flowing, you’ll need to clean the filters, turn on the circuit breaker, or repair/replace the motor or limit switch.
In this article, I’ll explain each of the problems that cause a lack of air blowing through vents, as well as walk you through the appropriate fixes. I’ll also let you in on the easiest way to fix your furnace. (Check the bottom of the article.)
Let’s get started!
Clogged or Dirty Air Filter
The first thing you need to check if your furnace isn’t operating correctly is to check if the air filter needs to be changed. Over time, an air filter can collect debris and dust and will need to be switched out.
On average, a furnace air filter will need to be replaced every one to twelve months, depending on size. However, this is highly dependent on the area’s air quality, the make of the furnace, and how large the filter is.
Here is a guide on how frequently you’ll need to replace air filters in a furnace:
|Filter Size (inches)||Replacement (months)|
How To Fix
- Determine the type of filter you will need to replace and get the corresponding filter.
- Turn off the power to your furnace by locating the on and off switch or by unscrewing the fuse.
- Open up your furnace and locate the filter location.
- Remove the current filter from the filter holder and discard it.
- Place a new filter into the filter holder and close the furnace.
- Turn your furnace back on and see if the problem persists.
Here is a video demonstration by ForDummies showing how to replace and test the furnace air filter:
Check Circuit Breakers
Another common mistake I see homeowners making is that the circuit breaker has been shut off. After a power outage or newly installed electrical wiring, your furnace circuit may have been cut off. When power is cut off, the whole furnace system will no longer receive electricity and shut down.
How To Fix
- Locate your home’s circuit breaker box and open it up.
- Identify the correct switch that corresponds to the location of your furnace and the blower motor.
- Turn the circuit switch on and check your furnace.
- If the furnace doesn’t turn on, check the main switch on the furnace to see if its switch is flipped on.
- If the switch immediately switches off or doesn’t start the furnace fan, then it’s likely there’s another problem with the system.
Broken Blower Motor
A broken furnace blower motor could also be the cause of air not blowing through vents. Furnace blower motors are responsible for dispersing air into your home via a Permanent Split Capacitator (PSC) or a Brushless Permanent Magnet (BPM) system. When a blower motor stops producing air, it’s likely due to one of the components breaking or shorting out.
However, most home furnace blower motors have a setting that automatically cuts off the air circulation when the temperature gets too high. This is mainly to help prevent a fire and to shut the system off if it overheats. The blower motor also has a thermostat that can be manually set to shut the unit off. So, it’s worth checking this first before jumping to the assumption that your furnace blower motor is damaged.
How To Fix
- Start by turning the main power source to the furnace off.
- Next, change the thermostat to its ‘fan only mode’ or switch heat to ‘off’ and fan to ‘on.’
- Wait a few minutes as this will give enough time for the furnace to start the fan entirely.
- The power will turn on, and the fan will begin to spin.
- If the fan doesn’t turn on at this point, you know there is a motor problem.
- Head back to the breaker and see if the furnace switch is flipped off.
- If the switch is flipped off, you will need to contact an HVAC tech or replace the furnace motor replacement, which typically costs anywhere between $400-$600.
- If the switch is turned on, then you’ll know that the settings were the issue.
Here is a video demonstration by Word of Advice TV showing how to replace the furnace blower motor:
Faulty Fan Limit Switch
A fan limit switch is a thermostat that is connected to the central HVAC system. The switch is wired to the fan and automatically stops the fan when the furnace reaches a specific temperature. The problem with this is that the limit switch may be broken or need to be replaced.
How To Fix
- Refer to your manufacturer’s manual for the type of limit switch installed.
- Next, shut off the main power to the furnace using the service switch or circuit breaker.
- Take the limit switch off by unscrewing any screws.
- Once you have it fully detached, attach the replacement switch.
- Put everything back together.
- Set the temperature to the ideal heat.
- Turn the power back on and test to see if the problem is fixed.
Here is a video demonstration by SuperCool Slide Rule showing how to replace and test the fan and limit control:
The Easiest Fix for a Furnace Not Blowing Air Through the Vents
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