This is a BRAND NEW OEM Lennox/Armstrong/Ducane Furnace HSI (Hot Surface Ignitor). Simply unplug yours and plug this one in! The Lennox/Armstrong/Ducane part # is 19W61. Thanks for looking and good luck!
The purpose of an ignitor is to ignite the gas after the gas valve opens up. It most cases, the ignitor turns off after ignition has occurred.