AKA: solar bypass
Anisolation valve should be a part of every solar water heater to isolatethe solar tank in case of a problem, while still allowing the backupwater heater to remain in service. The isolation valve is a manualvalve or valves placed in both the incoming and outgoing potable waterlines to the solar tank. It can be a three-valve configuration, or athree-port and two-port valve. Manually turning the valve or valveswill place the solar tank "on line" or "off line." It works bydirecting the flow either through or past the solar tank. These valvescan also be plumbed to bypass the backup gas or electric water heater,allowing them to be turned off (eliminating standby heat loss) duringthe seasons when the SHW system can supply 100 percent of thehousehold´s hot water.