The Weil McLain 640-000-028 3-Way Valve Combi Only is a replacement hydronic control valve designed for compatible Weil McLain combi boiler systems. It regulates and directs water flow between heating and domestic hot-water circuits, helping the boiler manage temperature and water distribution according to system demand. This valve supports efficient operation by controlling flow betw... https://www.partshnc.com/640-000-028-weil-mclain-3way-valve-combi-only