Navien Tankless Water Heaters 20017212A O-Ring P20 is a sealing component designed to create a secure, leak-resistant connection between compatible tankless water heater parts. It works by compressing between mating surfaces to prevent water leakage and maintain proper system pressure during operation. This O-ring is commonly used in Navien tankless water heaters and hydronic heating ... https://www.partshnc.com/20017212a-navien-tankless-water-heaters-o-ring