The Lochinvar & A.O. Smith 100110771 HSI/Flame Sensor Assembly is a crucial component found in gas-fired HVAC systems, primarily in furnaces and boilers. This assembly integrates a flame sensor and a hot surface ignitor (HSI) into one device. When electrical current flows through the assembly's HSI component, which acts as a dependable ignition source, it heats up and ignites the gas ... https://www.partshnc.com/hsi-ignition-assembly-3