Ignition System
The ignition system is the mechanism in a furnace that creates the spark or heat needed to light the fuel and start the heating process. Modern systems typically use electronic ignition rather than traditional standing pilot lights.
The ignition system serves as the starting mechanism for your furnace, responsible for lighting the fuel that generates heat for your home. This component has evolved significantly over the years, with modern furnaces using electronic ignition methods that offer improved efficiency and reliability compared to older pilot light systems.
Types of Ignition Systems
Furnaces use several different ignition methods, each with distinct characteristics:
- Hot Surface Ignition: Uses a silicon carbide or silicon nitride element that heats to extremely high temperatures (over 2,500°F) to ignite the gas. This is the most common type in modern furnaces.
- Intermittent Pilot: Creates a spark to light a pilot flame only when heat is needed, which then ignites the main burners. The pilot turns off after the heating cycle completes.
- Direct Spark Ignition: Generates a spark directly at the burners to light the gas without using a pilot flame.
- Standing Pilot: An older system featuring a continuously burning pilot light. While reliable, this method wastes energy and is rarely used in newer furnaces.
How the System Works
When your thermostat calls for heat, the ignition system activates before gas flows to the burners. The igniter heats up or creates a spark, and once the system confirms proper ignition temperature, the gas valve opens. The igniter then lights the gas, starting the heating cycle. A flame sensor monitors the burners to verify successful ignition and maintains safety by shutting off gas flow if the flame goes out.
Common Issues and Maintenance
Ignition systems can experience problems that prevent your furnace from starting. Hot surface igniters can crack or break due to their brittle nature when heated repeatedly. Spark igniters may fail due to electrical issues or dirty components. Regular cleaning and inspection help prevent many ignition problems.
Professional technicians check the ignition system during annual furnace maintenance, cleaning components, testing electrical connections, and verifying proper operation. Replacing a faulty igniter typically costs between $150 and $400, depending on the type and furnace model.
Safety Features
Modern ignition systems include multiple safety mechanisms. Flame sensors detect whether gas has successfully ignited, shutting down the system if ignition fails. This prevents dangerous gas buildup in your home. The system also includes lockout features that stop ignition attempts after several failures, requiring manual reset to prevent repeated unsafe conditions.
