The System Controller is necessary when you're connecting 3 or more identical units together. This controller allows multiple tankless water heaters to communicate off of one remote controller.
PART #: SC-201-6M (up to 6 units)
Installation manual
PART #: SC-201-12M (up to 12 units)
Installation manual
PART #: SC-201-24M (up to 24 units)
Installation manual