Why Furnace Inducer Fan Runs But Won’t Ignite

The inducer motor is a critical part of the gas furnace. It helps vent toxic gases from the burner to protect you from gas poisoning and the furnace from potential rollout flames.

Moreover, the inducer motor ensures a constant supply of airflow inside your home to prevent the buildup of toxic gases within the home. 

For these reasons, the inducer motor is usually the first kick ON when you turn ON the gas furnace. Typically, it will run for 60 seconds before actual heating begins. 

But what if heating doesn’t follow? What if the inducer motor has been running for two minutes straight without a sign of heating? 

Of course, it would present all kinds of challenges. For one, it would leave you in the biting cold, perhaps on a freezing night. Getting to morning in such conditions is akin to walking on hot coal. More importantly, when the exhaust blower runs but the heat doesn’t come ON, it can cause significant alarm. 

Are the heating elements broken? Is it the limit switch? Or perhaps the unit sensed a buildup of carbon monoxide in the home and is trying to clear the toxic gas before resuming heating? These are just some of the questions that would run across your mind. 

Read on to find out how the inducer motor works, its role in the heating system, why it would run without heating, and what you can do. 

What’s an Inducer Motor?

When you start your gas furnace, the flames don’t just start to burn right away. It can take up to a whole minute between pressing the furnace ON button and seeing feeling the heat come out from the ductwork. 

Essentially, nine things take place, sequentially, before you can feel hot air coming through the air ducts;

  1. You press the switch to turn the furnace ON
  2. The control board receives power from your electrical system
  3. The thermostat takes current temperature readings and sends a request for heating
  4. The inducer motor kicks on
  5. The pressure switch confirms that the inducer switch is running and alerts the ignition system
  6. The ignition system kicks on (and lights the pilot light)
  7. The gas valve energizes and allows gas to reach the burners
  8. The burners light up
  9. The flame sensor proves that all burners are lit
  10. The blower fan forces hot air through the vents and into your home

So, as you can see, the inducer motor is one of the first things that kicks on when you switch on your furnace. Immediately you switch on the furnace, it sends 120 volts of electric current through the wires from the control board to the inducer fan, causing the fan to start rotating. Sometimes the inducer fan can run for up to 20 seconds before anything else happens. 

Why so? Because the inducer valve serves as a safety feature. The primary purpose of the inducer fan is to rid the furnace of poisonous gases from the previous heating cycle. It moves harmful gases, such as carbon monoxide, out of the heating system and your home to prevent poisoning. 

Additionally, the inducer fan’s cycling prevents the furnace burners from becoming clogged with soot. Without the blowing motion, soot can live on the furnace for a long time, weakening the furnace’s internal parts while also causing havoc inside the home. Getting rid of the stale air before heating begins guarantees that the warm air coming from the vents is clean and safe. 

6 Reasons Why Inducer Motor Runs but No Ignition

Now that we know what the inducer motor is and what it does, it’s easy to troubleshoot an inducer that runs without producing heat. In many cases, you’ll find that it’s one of the following issues;

1. Poor venting 

Poor venting essentially means that the motor finds it challenging to remove combustion air from the ductwork and your rooms outside the house. Venting issues usually result from two challenges;

2. Blocked vents

Your furnace uses vents to eliminate combustion air outside the home. Indeed, many homes have a special pipe/vent through which combustion air exits the home. If not, the furnace will rely on openings within the home, including the doors and windows, to vent stale air. 

If these vents or openings are closed or blocked, the inducer motor may struggle to remove carbon dioxide and other gases from home, causing it to run for an extended period before the furnace kicks ON. 

Fortunately, it’s a problem you can resolve with ease. Check the vent to make sure it’s not blocked. If it is, clean it as appropriate. Also, make sure there’s enough ventilation in your rooms to let out stale air. 

3. Dirty filters 

Another issue that can cause venting issues is dirty filters. As mentioned, the inducer fan is also responsible for creating airflow to eliminate combustion air outside the house. So, it needs to pass cold air from the house into the furnace and out through the supply ducts.

However, the return ducts where cold air passes when entering the furnace are fitted with filters to clean the air as a mechanism to protect the furnace’s internal components.

If these filters are dirty, cold air might encounter challenges trying to pass through. This can cause the inducer motor to run for longer as it attempts to achieve the desired airflow. 

Here too, the solution is easy. You need to clean your furnace filters regularly as directed by the manufacturer. Typically, it would help if you cleaned it at least once every month. For single-use filters, you need to replace them once every 1-3 months. 

4. Thermostat not set correctly 

The draft inducer vent may also cycle longer than usual if the thermostat setting is wrong. This, too, is a straightforward matter. 

When you start the furnace, the thermostat instructs the unit to heat the room to a pre-defined temperature as set by the user – unless you’ve set it to AUTO – which most experts don’t recommend. Many experts will tell you to set the thermostat to “Heat” and the fan to “Auto” for the best experience. 

However, a few things can go wrong. For one, the user can mistakenly input the wrong temperature setting. For instance, you may leave the thermostat at 50°F when you should have it at 68°F to 72°F, according to the Department of Energy. Alternatively, you may have a malfunctioned thermostat that keeps jumping from one value to another. 

Whenever the temperature setting on the thermostat is lower than room temperature, the furnace will not work. So, no matter how long the inducer motorcycles, you won’t see any heat. 

5. Ignition system has malfunctioned 

If the thermostat is working well and set correctly, then you need to check the ignition system. As we’ve seen, the ignition process comes a little later after the draft inducer motor has run for up to a whole minute. So if the ignition process encounters an issue, the inducer motor may run without anything else happing.

So, what could go wrong with the ignition system? A lot! First, maybe the pilot system has malfunctioned. Perhaps it’s dirty, thus cannot light. Or maybe it’s blocked. In this case, you need to clean the pilot system. 

Another possibility is a malfunctioned flame sensor. The flame sensor verifies the presence of the pilot flame and burners flames and can cut the power supply to the furnace control board if it can’t sense a flame in either case.

However, the flame sensor (thermocouple) can become dirty and even malfunction, leading to erroneous sensing. If the unit can’t sense a flame, the inducer motor may keep running without the burners coming ON. Cleaning the flame sensor or replacing it altogether will fix this issue. 

6. The inducer motor is bad 

Despite its reasonably simple construction, the fan inducer motor has the highest failure rates of any part of the furnace. One of the signs of a malfunctioned inducer motor is running without heat from the furnace. 

As soon as the furnace detects that the inducer motor has malfunctioned, it will shut down and discontinue the heating process. This is a safety mechanism meant to protect both the furnace and the home’s occupants. If the furnace continues to run with a defective inducer motor, there’s a significant risk of carbon dioxide and other poisonous gases. 

Fortunately, it’s easy to diagnose a defective inducer motor. First off, as we’ve just mentioned, the furnace will likely go off. It may come on then go off almost immediately.

Or it may refuse to come on altogether. Additionally, a defective inducer fan makes characteristic tapping noises as the bearings in the motor click together. The unit may also vibrate a lot. 

The only solution to a defective inducer motor is to replace it as most units are impossible to rebuild after they’re damaged. 

If you’ve tried all the solutions discussed here, but the inducer motor keeps running without producing heat, it’s time to call the pros. 

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