How It Works

• Electronic ignition systems are common on more recent furnaces, replacing older pilot lights. When activated by an electric current, the surface of the glow plug heats up and ignites the burners in the furnace.
  
  

Damage

• Cracks may occur in a glow plug during shipping or over time. A cracked plug may still be operational, but it may not last for long. The cracks may be hard to detect unless the glow pattern is checked.
  
  

Other Facts

• Glow plugs vary by design, materials, voltage and required warm-up, depending on the furnace manufacturer. They should not be used for furnaces other than those for which they are designed.