The Weil McLain 640-000-019 Water Pressure Switch with Mount is a replacement safety and monitoring component designed for compatible combi boilers and hydronic heating systems. It works by continuously sensing water pressure within the system and signaling the control board when pressure levels fall outside the required operating range. This helps protect critical boiler components f... https://www.partshnc.com/640-000-019-weil-mclain-kit-s-swchwtr-press-wmnt-combi