Flame Sensor Vs. Ignitor: What’s The Difference?

It's time for furnace maintenance; perhaps the unit's flame sensor or ignitor needs a replacement. Since both parts are very similar, it is a challenge for you to identify which is which. Also, knowing both components' differences and functions helps prolong their life span. You're on the right page! See what our research has discovered about flame sensors versus ignitors.

The main difference between a flame sensor and an ignitor is their functions. Although both work together to provide safety measures in your furnace system.

The flame sensor detects whether a fire is present in the burner. It also cuts off the gas supply when it confirms that the burner's flame is out.

Meanwhile, the ignitor is what causes the gas or fuel coming from the burner to ignite. Without the ignitor flame, this would be impossible.

Did you know that the latest furnace systems use different types of ignitors? Perhaps you still want to learn whether you can clean your flame sensor and the correct cleaning procedure. Don't miss out, keep on reading! 

A propane furnace, Flame Sensor Vs. Ignitor: What's The Difference?

How Does A Furnace Flame Sensor And Ignitor Function?

A flame sensor is a safety device that can sense a flame when your furnace is on. Its function is crucial in the event that flames are out while the gas supply is still flowing. This could result in a fire disaster and risk your family's life.

Its operation involves sending signals to the system controller to open the gas or fuel valves from its combustion chamber. It has a timer that activates when you try igniting the burner.

Now the sensor ignores the "no flame" reading unless the metal rod detects a flame. After the countdown expires, the controller cuts off the gas flow if it doesn't sense a flame. The flame sensor will keep cycling the process as it always instructs the system to supply gas until the flame goes off.

In contrast, in the past decades, furnaces, especially those in residential settings used pilot lights to light the flame. However, modern furnaces are now using an ignition system consisting of various igniters to start a flame. During a call for a flame, the igniter runs an electric spark to begin the combustion process.

The Four Common Types Of Furnace Ignitor

Like your flame sensor, ignitors also play a vital role in starting heat in your furnace when you need to warm your house. The type of ignitor you have will always depend on the brand and model of your furnace.

Here are the four main types of ignitors that your furnace uses:

The Hot Surface Ignition System (HSI)

The hot surface ignition system is fuel-efficient; it only burns fuel when the furnace unit is operating. Besides, it also has a draft blower motor to ensure that combustion waste will properly exit your home.

The Direct Spark Ignition System

This ignition system ignites the flame via an electrical spark through a DC source, but the oscillator has total control. It employs several safety devices to operate perfectly, like a spark generator to accurately ignite the burner.

A propane furnace

An inverter safely changes the DC voltage into a high AC voltage. An ignition coil that connects the capacitor and switch is responsible for creating a pulse in your coil.

The Intermittent Pilot Ignition System

This ignition system was considerably popular during the second half of the 1900s. That time was the revolutionary period in producing intermittent pilots in most furnaces units.

Standing Pilot Ignition

Among the other ignition systems, the standing pilot has the most straightforward design. Its burner has a gas line which also creates a flame.

This system uses a small metal wire known as a thermocouple that links the burners to a valve in the gas pipe. The thermocouple sends an electric signal to control the combustion and shut off the gas valve when the flame goes out.

Where Is The Location Of The Flame Sensor And Ignitor?

Given that the flame sensor and ignitor are both small metal rods, knowing these components' locations is crucial during the maintenance procedure.

Generally, the flame sensor is in the burner's chamber, opposite the position where the ignitor is also set in place. As you know, it is a thin stick or rod, and most often, it appears to be bent.

In contrast, you'll see your furnace ignitor housed directly in the gas port's bracket. You can easily identify it due to its lower back portion having two wires with a flat metal edge. What's more, its physical body resembles a 'V' shape.

How Do You Know If Your Flame Sensor And Ignitor Are Going Bad?

The furnace system's flame sensor and ignitor are also subject to failure like any other part of HVAC appliances. You can use a multimeter to tell precisely that both components are in good condition.

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Still, it reveals early symptoms before it suddenly stops functioning properly. After all, servicing your furnace system yearly will prevent its vital parts from failing sooner than they should.

Flame Sensor Going Bad

The following are the common signs that your flame sensor is becoming bad:

  • If its burners are burning flames for a moment and abruptly cease, likely its flame sensor is already bad.
  • Once the sensor rod has visible soot buildup that covers the tip of the sensor, then it is bad.
  • Either the flame sensor's porcelain casing is cracked, or the flame sensor's edge is full of dirt or completely black.

Flame Ignitor Going Bad

On the other hand, these are the symptoms of a malfunctioning ignitor:

Changing the thermostat level

  • Upon verifying that your thermostat is in the right thermal setup. When your furnace begins blasting cold air, chances are your ignitor is at fault.
  • A bad ignitor won't provide enough charge to support the burning process. So, you'll notice that the furnace randomly starts and shuts off again. Until then, it is safe to conclude that you're dealing with a bad ignitor.
  • Another obvious symptom is the breaker which powers the furnace always trips.

Remember that, you should ensure as well that the system ignitor needs a sufficient voltage to run properly. Modern ignitors need 110-120 volts to support the ignition cycle of a blower motor in a furnace. Making sure your furnace system can handle the initial ignition process helps avoid short cycling your furnace.

How Much Does A Flame Sensor And Ignitor Replacement Cost?

A gas propane furnace burner photographed up close

Anything can go wrong if you keep repairing completely bad furnace components, such as the flame sensor or ignitor. It is always a great idea and the most practical solution to replace faulty parts.

Depending on your local market, furnace brands, and technician service charges, you can prepare to spend $350-$500 for a new flame sensor.

However, a new igniter will only cost around $120-$365. Also, don't forget to check your warranty if your ignitor is still within its coverage. Using the warranty means you'll at least pay only a labor fee of $150.

Can I Clean The Flame Sensor: How To?

Over time, your flame sensor will inevitably undergo wear and tear, especially oxidation and corrosion formation in the flame sensor rod. Replacing or cleaning it is the least option to put it back to being functional again.

Buy this flame sensor on Amazon.

Fortunately, you can avoid another expense because you can clean a severely dirty flame sensor. You can use steel wool, cloth, or even mild sandpaper to clean the dirty sensor.

Here are the cleaning steps you can follow:

  1. Start by shutting the entire power supply in your furnace unit.
  2. Open the combustion cell door to access the flame sensor.
  3. Gently detach the flame sensor from its bracket.
  4. Start removing the flame sensor debris using steel wool, light sandpaper, or any cloth you have.
  5. Now wipe any remaining dirt in the flame sensor.
  6. Conduct a quick cleaning as well to the furnace electric igniter before reinserting back the flame sensor.
  7. Ensure to properly close the combustion cell's door.
  8. Lastly, switch on again the furnace unit's power supply.

CAUTION! If these cleaning steps didn't work, we highly suggest calling your HVAC specialist to get extra advice.

A gray Goodman furnace in the basement

How Long Does A Furnace Flame Sensor And Ignitor Last?

Under proper maintenance guidelines, you can expect your furnace flame sensor to last about five years. The furnace ignitor has a life expectancy of roughly four to seven years. Furthermore, maintaining your flame sensor and ignitor regularly guarantees to safeguard your furnace system more than its expected life span.

In Closing

A propane furnace

Knowing the distinct differences between a furnace flame sensor and its igniter will give you a better understanding of how they operate. This will also help you determine what kind of maintenance these parts require to keep their condition at peak. Sharing all of this knowledge with you will ensure the components of your furnace last longer.

Before you go, kindly visit as well our other helpful article below!

No Power To Furnace – What To Do?

Do Propane Furnaces Have A Pilot Light

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