Tankless water heater isolation valve assembly

An isolation valve assembly, which comprises:

• a valve body defining a first fluid port and a second fluid port opposing the first fluid port, at least one drain port disposed between the first fluid port and the second fluid port and a plug valve port, wherein the first fluid port comprises a fluid inlet port and the second fluid port comprises a fluid outlet port;
• an isolation valve plug disposed through the plug valve port and within the valve body, the isolation valve plug being rotatable relative to the valve body and carrying a pair of opposing plug seals;
• and
• a handle operatively coupled to the isolation valve plug, the handle movable to cause corresponding rotation of the isolation valve plug between a first normal position in which the fluid inlet port is fluidly coupled to both the fluid outlet port and the at least one drain port, and a second drain position in which the fluid inlet port remains fluidly coupled to the at least one drain port and one of the pair of opposing plug seals closes the fluid outlet port to isolate the fluid outlet port from the fluid inlet port.