Where is the Flame Sensor on a Furnace?

The flame sensor is a vital part of your furnace. If it’s broken or dirty, your furnace will cease to operate.

The flame sensor is in burner assembly on your furnace. It’s normally at the bottom of your furnace and is a thin metal rod in front of the pilot light that’s bent.

It may be attached with a hex screw, so you’ll need to remove to access the flame sensor.

Below you’ll find out what a flame sensor does, how to clean it, and signs your flame sensor is malfunctioning.

Let’s get started.

Where is the Flame Sensor on a Furnace?

The flame sensor on your furnace is in the burner assembly. It’s a thin metal rod that’s usually bent and in front of the pilot light inside of your furnace.

The burner assembly is typically at the bottom of your furnace.

What does a Flame Sensor Do?

A flame sensor is a vital part of your furnace system. When your furnace is lit, it uses a spark or a hot surface ignitor that lights the gas.

The flame sensor creates a current of electricity that’s used to sense if there is a fire starting within your furnace.

If the flame sensor does not detect that the flame is working as intended, it will shut your furnace down.

This is to prevent any explosions and keep your furnace working properly. If your flame sensor becomes dirty, then your furnace will cease to operate.

How to Clean Your Furnace’s Flame Sensor

1. Turn off the electricity and gas valve

Before you proceed with cleaning your furnace’s flame sensor, you must shut down the power to your furnace.

There should be a toggle switch that’s near your furnace (looks like a light switch).

If you don’t have a toggle switch, shut your furnace down via the circuit breaker.

If your gas is not controlled electronically, then shut down the gas as well before proceeding.

2. Remove the flame sensor

To remove the flame sensor, you’ll need to remove the screw that’s mounting the flame screw. It’s typically a 1/4″ hex head screw.

Once you remove the screw, you’ll be able to slide out the flame sensor so that you can clean it. You may have to detach the wire to fully remove the flame sensor.

3. Clean your flame sensor

Once you’ve removed the flame sensor, you’ll need to rub the metal rod with light grit sandpaper.

You’re not trying to sand down the metal rod, but rather removing any built-up grime or grit that’s preventing the flame sensor from operating normally.

4. Return the flame sensor

Once you’ve cleaned the sensor, reconnect the wire and screw back on the screw that you removed.

Put the door back on the burner assembly and turn on the gas and electricity and your furnace.

Signs Your Flame Sensor is Bad

Furnace short cycles

If your furnace turns off and on quickly, then this is a sign of a bad flame sensor.

If your furnace flame sensor is faulty, it will shut down your furnace as it won’t be able to detect that the fire is lit.

The flame sensor is cracked

If you’ve taken out your furnace flame sensor and noticed that it’s cracked or warped, this can be a sign that it’s malfunctioning.

The porcelain on the outer part of the flame sensor is what detects the heat, and if it’s cracked, it won’t work properly.

Your flame sensor is dirty

Over time, a dirty flame sensor can become corroded to the point that it no longer works.

If you’ve tried to remove the corrosion or dirt and it still isn’t working properly, then your furnace flame sensor must be replaced.

When to Replace Your Furnace Flame Sensor?

Most furnace flame sensors should last about five years.

The average furnace lasts about 15-30 years, so you should expect to replace the sensor a few times during your furnace’s lifetime.

If your furnace hasn’t been serviced in a while and is short cycling, it may be time to purchase a replacement flame sensor.

Furnace flame sensors cost less than $20 but you will have to install them yourself.

If you hire an HVAC technician, then you should expect to pay anywhere between $60-250 depending on where you live.

When to Call an HVAC Technician?

You should call an HVAC technician if your gas furnace is having issues working properly. If you aren’t sure of how to troubleshoot your furnace, then you shouldn’t take any chances working with a dangerous device.

To set up an appointment with a local HVAC technician, simply click the button below, and you’ll be given a free quote in a matter of minutes.

Final Thoughts

A faulty flame sensor may seem like a huge problem, but in reality, it’s a cheap fix.

If you’ve tried cleaning your flame sensor but still have issues with your furnace, it might be time for a replacement.

If you decide to fix the flame sensor yourself, ensure that you turn off the gas and electricity before working on your furnace.

Your flame sensor being dirty can also lead to your furnace blowing cold air.

Image Credit: Flickr.com

About Roy Cohen

Roy Cohen has a burning passion for heating, cooling, and ventilation. He aims to help you save money on expensive repairs and bring you the best HVAC products. He has years of experience behind him in HVAC repair and garage maintenance.

You can find Roy at his LinkedIn or his email: [email protected]

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