Having the pilot light lit while the furnace won’t kick on can be somewhat complex. Many factors can contribute to this problem, so it is vital to troubleshoot each one systematically to determine the root cause.
This guide will talk about the most common causes of this issue, such as a faulty igniter, clogged burner, or dirty flame sensor. We will also provide step-by-step instructions on how to fix each problem.
Keep on reading to find out more about this furnace issue and the best ways to solve it permanently.
Why is the pilot light lit but the furnace won’t kick on?
The role of the pilot light in the furnace is to help in providing a constant supply of flames. It is used to light the burners in the furnace.
The pilot light usually uses a small amount of gas to create a flame, which is then used to ignite the larger supply of gas needed to run the furnace. If the pilot light goes out, the furnace will not be able to produce heat.
However, if the pilot light is lit but the furnace won’t kick on, a couple of underlying issues could jeopardize the furnace system.
Here are some of the most common causes behind this issue.
Faulty igniter
The most common reason for a faulty igniter is that it has become corroded or damaged. If your igniter is not sparking, it may be because it is not getting enough power.
Dead or malfunctioning batteries are one of the most common issues with a malfunctioning igniter. Over time, the batteries in your igniter will begin to lose their charge and won’t be able to provide enough power to create a spark.
Another possibility is that the wire connecting the igniter to the battery is damaged. This wire can become worn down over time, and if it’s not replaced, it can eventually cause the igniter to stop working.
If you’re not getting a spark at all from your igniter, it’s likely that it needs to be replaced.
Clogged burner
Your furnace may not be able to kick on due to a clogged furnace burner. This is usually caused by a buildup of dirt and dust on the burner and can be easily fixed with a good cleaning.
Most furnaces have an access panel that will allow you to get to the burner for cleaning. If you don’t clean the burner regularly, it will become clogged with soot, and eventually, it will not work.
If your furnace has an access panel, open it up and look at the burner. If you see any accumulated soot or dirt buildup, this may be the reason why the furnace isn’t kicking on.
Dirty or malfunctioning flame sensor
A dirty or malfunctioning flame sensor is one of the most common reasons for a furnace to shut down. This sensor is a safety device that tells the furnace whether or not a flame is present.
If the sensor is dirty and unable to detect the flame, it will shut down the furnace. A malfunctioning flame sensor will also prevent the furnace from kicking on, even though the pilot light is lit.
If your furnace keeps shutting down or won’t kick on, be sure to check the flame sensor.
Thermostat set too low
Your furnace may not be able to kick on because the thermostat is set too low. The role of the thermostat is to signal the furnace when to turn on and off, depending on the room temperature.
The thermostat will never prompt the furnace to turn on if it is set below room temperature.
Defective gas control valve
If you have a defective gas control valve in your furnace, it is essential to have it replaced as soon as possible. A faulty gas control valve can cause several problems, including a gas leak, which can be dangerous.
In addition, a defective gas control valve can also prevent your furnace from heating properly, wasting energy and money.
The role of the gas control valve is to regulate the flow of gas to the burner. It is usually located near the burner or pilot light.
Corroded burner line and jet
A corroded burner line can cause your furnace to operate less efficiently, and a too-small jet can cause your furnace to overheat.
The role of the burner line in a furnace is to deliver the fuel to the burner. The size of the burner line is also quite important, as it needs to be large enough to have the right amount of fuel for the burner.
If the burner line is too small, the furnace will not be able to operate at its full potential. Too small of a jet, on the other hand, will limit the heating ability of your furnace.
The jet in a furnace is responsible for igniting the fuel. The size of the jet is an essential factor, as well, because it needs to be large enough to provide a good, intense flame.
How to fix a furnace that won’t kick on with the pilot light lit
When it comes to more complex, gas-related issues, we certainly recommend not tackling any of these on your own.
Proper troubleshooting often calls for professional assistance, so you may want to hear a second opinion before you decide to try any of the fixing methods for your heating system.
Let’s dive into the best techniques for fixing a furnace that won’t kick on even though the furnace pilot light is lit.
1. Replace the faulty igniter
If your furnace’s igniter is faulty, it must be replaced. Igniters are not repairable, so you’ll need a replacement from a heating and cooling parts supplier.
However, get the correct model for your furnace before entering the installation process.
Before beginning this repair, ensure you have disconnected the power to your furnace. This is a necessary safety precaution that should not be ignored.
Once you have the replacement igniter, follow these steps to install it:
- Remove the old igniter: Start by removing the screws that hold the old igniter in place. Carefully pull out the old igniter, being careful not to damage any of the surrounding wires or components.
- Install the new igniter: Position the new igniter in the same spot as the old one, and secure it with the screws. Be sure not to overtighten the screws, as this could damage the igniter.
- Reconnect any wires that were disconnected: Once the new igniter is in place, reconnect any wires that were disconnected during the installation process.
- Test the new igniter: Before you put the furnace back together, it’s essential to test the new igniter to ensure it’s working correctly. Turn on the furnace and see if the igniter glows brightly. If it does, the installation was successful. If not, you may need to repeat the process.
- Put the furnace back together: Once you’ve tested the new igniter and confirmed that it’s working correctly, you can put it back together. Replace any removed panels or covers during the installation process, and ensure all screws are tightened securely.
- Reset the furnace: Once it is back together, you’ll need to reset it. Consult your manufacturer’s manual for specific instructions on how to do this. In most cases, you’ll need to turn off the power to the furnace, wait a few minutes, and then turn it back on.
- Test the furnace: Once the furnace is reset, you should test it to ensure it’s working correctly. Turn on the power and set the thermostat to your desired temperature.
The furnace should kick on and begin heating your home.
2. Clean the clogged burner
In some cases, a clogged burner can even cause your furnace to shut down completely. You can clean your furnace’s gas burner with just a few simple steps.
First, turn off your gas furnace and allow it to cool completely. Next, remove the burner assembly from your furnace. Be sure to disconnect any wires or tubes attached to the burner before removing them.
Once the gas burner assembly is removed, use a brush or vacuum to clean away any dirt or debris clogging the burner.
Pay attention to the area around the fuel inlet, as this is often a significant source of burner clogs.
Once the burner is clean, reassemble the furnace and turn it back on. You should see an immediate improvement in your furnace’s performance.
However, if the clog is severe, you may need to repeat this process periodically to keep your gas appliance running smoothly.
3. Clean the flame sensor
Over time, the flame sensor can become coated with dirt and debris, preventing it from working correctly. If your furnace isn’t firing up when it should, or if the pilot flame goes out often, try cleaning the flame sensor.
You’ll need a small brush or an old toothbrush to clean the furnace flame sensor. Gently scrub the sensor with the brush to remove any dirt or debris.
Once you’ve cleaned the ignition sensor, reattach it to the furnace and turn it on. The furnace should now operate correctly.
4. Adjust the thermostat settings
Your thermostat may be set too low, preventing the furnace from kicking on. To adjust the thermostat, find the knob or slider on the front of your device and turn it to a higher setting.
Once you’ve increased the temperature, wait a few minutes to see if your gas furnace starts up.
5. Have the gas control valve repaired or replaced
A faulty gas valve is a severe furnace problem that should ideally be tackled by a professional.
Have a licensed technician inspect and test the gas control valve, then have it repaired or replaced depending on the severity of the issue.
6. Inspect the burner line and jet
Finally, you must inspect the burner gas line and jet if your gas appliance isn’t kicking on. If you can see that the furnace pilot light is out, you will likely need to relight it.
However, the burner gas line may be clogged if the pilot light is lit. You can try cleaning it out with a wire brush, as long as it isn’t damaged.
On the other hand, if the jet is clogged, you may need to replace it.
Adrian is an ISCET licensed professional that has completed the National Appliance Service Technician Certification Exam and has the expertise to diagnose and repair any appliance. He is well-versed in the latest technologies and techniques and is always up-to-date on the latest industry standards.
