Caleffi's iSolar 257 Series is an attractive, compact, easy-to-install, multi-functional temperature differential controller with add-on system functions. It can be used for a wide variety of applications and has inputs for four sensors. Preset factory defaults control a standard solar water heating system with a second relay (some models) to divert surplus heat. The auxiliary relay can maintain tank temperature, protect the system from overheating, or direct another source to heat the storage tank.

For more information,