The Navien Ready-Link Communicating Cable (GXXX000546) is a specialized communication accessory designed to connect multiple Navien tankless water heaters and compatible HVAC heating equipment. It enables communication between interconnected units, allowing them to operate together in a cascade configuration and support common venting applications. Compatible equipment includes Navien... https://www.partshnc.com/gxxx000546-navien-tankless-water-heaters-ready-link-communicating-cable