A gas furnace needs some type of system to ignite the gas or the combustion process cannot take place. Depending on the age of your gas furnace, the type of furnace ignitor may have been different. A very old furnace may still have a traditional pilot light and newer models may have a spark ignitor or a hot surface ignitor. In this article, we will take a closer look at furnace ignitors and how to clean them to improve performance and efficiency.

A Brief Furnace Ignitor Overview

For most of the 20th century, the ignition was created with a standing pilot light. The pilot light would burn continuously with a trace quantity of gas and combustion could take place when required. The main drawback to this system was that if the pilot light went out, it would need to be relit before heat could be generated. At the end of the century, some manufacturers switched to a new ignition system that uses a spark ignitor. At first, the spark ignitor would light the pilot light, and eventually, they replaced them entirely. The modern variant is a hot surface ignitor that has a resistive heating element that warms up and glows red hot to cause combustion.

The Different Types of Furnace Ignitors

As we mentioned in the introduction to this article, it’s unlikely that you have a pilot light without some kind of spark ignitor system. A pilot light alone would only be found on very old furnaces that would have such poor efficiency at this point, they would be unusable. A pilot light furnace would be an inefficient way to ignite a modern furnace in any event and as an older technology it’s the least efficient method.

A modern high-efficiency furnace will typically have an annual fuel utilization efficiency (AFUE) rating of 90 or more. This type of furnace will usually have a hot surface ignitor to start the combustion process. In fact, many gas furnaces with standard efficiency ratings have hot surface ignitors too. If you can hear a clicking noise when your furnace starts this means that you have a spark ignitor instead. If a spark ignitor is not working as intended, it can be cleaned to get it working again. But, this is a sensitive component, it has a pretty short lifespan and in many cases it makes more sense to replace it.

Which Type of Furnace Ignitor Do You Have?

When you know what to look for, it’s pretty easy to identify the type of furnace ignitor you have installed in your gas furnace. First, locate the access panel and you should be able to see the gas burners directly behind the panel opening. A domestic gas furnace typically has four burners, one end is exposed and the opposite end extends into the combustion chamber behind a metal wall. The ignitor is typically mounted on this metal wall somewhere close to the first burner unit. This burner is usually the unit that’s closest to the gas valve which should be visible.

Take a close look at the ignitor. If it has a white or yellow porcelain base and a long metal bar that extends into the first burner, it’s a hot surface ignitor. The metal bar has a pair of electrodes and this is the point where the spark is created. When this component is new the base is totally white, but over time it fades to a darker yellow color.

If you have an older gas furnace, you will notice a burner chamber and there should be a blue flame inside. If the pilot light is out, you may find it by following one of the two copper tubes that connect it to the gas valve. The pilot light can be ignited and the full instructions are in the owner’s manual for your furnace.

Both spark and hot surface ignitors have a pair of wires attached to them to supply power to create the spark.

How to Clean the Gas Ignitor with Compressed Air

Over time, an accumulation of burnt carbon deposits can form on the surface of furnace ignitors. This material can slow the start-up of a gas furnace or prevent the combustion process entirely. It may be possible to fix this without replacing the ignitor with gentle cleaning. One proven approach is to blast the carbon of the surface of the ignitor with a can of compressed air. This minimizes contact with the ignitor to prevent damage during the cleaning process.

Although a hot surface ignitor will continue to work when dirty much like the heating element on a stove it won’t work efficiently. A can of compressed air that you may use to clean other electronics in your home usually has a long plastic applicator tube. This allows you to deliver a blast of compressed air on a very localized point. Simply point the applicator end at the ignitor probe and give it a few blasts to see if the carbon comes away.

If you have a gas furnace that uses a spark ignitor and it’s working in an intermittent way, this could mean that it’s covered with a layer of soot. Again, applying a few blasts of compressed air to the ignitor may remove enough soot to get the component working again. If you have a blocked pilot light tube that causes the pilot light to burn weak or fail to light, you can use compressed air to clean the tube. Just point the applicator into the pilot light chamber and deliver a few quick blasts. Then light the pilot light to see if the cleaning was effective.

How to Physically Clean a Hot Surface Ignitor

It is possible to physically clean a hot surface ignitor if the compressed air method didn’t work. First, shut-off the power supply to the furnace at the main breaker panel or at the nearby wall switch. Then disconnect the hot surface ignitor wires, loosen the screws on the unit and carefully lift it out. This is a fragile component, treat it gently or it may break and you will need a replacement. Don’t touch the element with bare hands because skin oil will cause damage to older hot surface ignitors. To clean the unit, rub the probe with an emery cloth or fine steel wool to remove the burnt carbon. When it looks clean replace the ignitor, hook up the wires and restore power to the furnace. The ignitor can be tested by turning up the thermostat to get the gas furnace started.

If you have  a gas furnace ignitor problem or your furnace needs a tune-up, contact your local heating and cooling specialist today.