The furnace ignitor and furnace burners are the heart of a forced air heating system. One ignites the fuel while the others heat the air. 

By Anne Fonda

A furnace ignitor is a vital part of a gas furnace or oil furnace that starts the combustion process by heating the gas or oil until it ignites. 

Older furnaces have a standing pilot light to keep the gas lit. These have been phased out due to their inefficiency and safety concerns. Newer furnaces have an electronic ignition system. The most common type is the hot surface ignitor (HSI). Ignition happens in a sealed combustion chamber to protect you from exhaust fumes.

With an HSI, when the thermostat calls for heat, an electric current heats a piece of metal within the ignition system until it’s hot enough to combust the gas that started flowing with the call for heat. Trane furnaces use a silicon nitride hot surface igniter. This highly reliable gas furnace ignitor provides a longer service life.

Furnace burners work much like the burners on a gas stove. Once the gas is ignited, the burners heat one or more heat exchangers, which in turn heats the air. That heated air is then pushed into the ductwork by the blower fan. 

Trane furnaces have multi-port in-shot burners to perfectly shape the flame cone for the maximum heat possible while using less fuel. They’re enclosed in a sealed combustion chamber that receives air vented in from the outside. Older furnaces use an upshot burner with natural draft venting.

Once the set temperature is reached, the thermostat will signal a single or two-stage furnace to shut off. A high-efficiency furnace, or condensing furnace with a modulating gas valve, may run longer at a lower capacity to provide greater comfort and fuel efficiency. 

Signs of a bad or faulty furnace ignitor include:

• Furnace blowing cold air
• Furnace short cycling
• Furnace hard lockout

These symptoms can be caused by other furnace problems as well, including a problem with the furnace burner or limit switch. If the ignitor is to blame, furnace ignitor replacement is the solution. 

Signs of a malfunctioning or clogged furnace burner include:

• Insufficient heat
• No heat
• Strange sounds when the furnace comes on
• Higher gas bills

These symptoms can also be caused by other furnace problems. Check out our furnace troubleshooting page for helpful tips on figuring out what’s wrong with your furnace and when to call in HVAC professionals for furnace repair. 

To keep your furnace running at peak performance, make sure you keep up with regular furnace maintenance. Change the air filter regularly - every 30-90 days depending on the filter. Check out our air filter maintenance guide for some tips.

Schedule a yearly furnace tuneup every fall before the heating season begins. At that visit, your HVAC technician will do a thorough inspection of your furnace, clean the burners, check the ignition system, and more. Regular maintenance results in increased energy efficiency and enhanced heating performance and can extend the life of your furnace. 

Anne Fonda, Content Writer

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A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.

When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by John Kim, Senior Product Manager, Furnaces