The Lochinvar & A.O. Smith 100338900 ON/OFF Switch is a replacement electrical control component designed for compatible water heating equipment. It works by opening or closing an electrical circuit, allowing the connected system to be switched on or off as required. This switch is used in compatible Lochinvar and A.O. Smith commercial or residential water heaters and related heating ... https://www.partshnc.com/100338900-lochinvar-a-o-smith-on-off-switch