A control system for managing and interfacing a plurality of water heaters, e.g. boilers. The control system includes a first boiler unit controlled by a first boiler control unit and a second boiler unit controlled by a second boiler control unit. The first boiler control unit is operable to coordinate the operation of the first and second boiler units in response to changes in output demand. The flues of the first and second boiler units are connected to a common flue. The control system further includes an interface and an interface control system. The interface control system communicates requests from the interface, to report and/or alter the operating parameters of the first and second boiler units, to the first and second boiler control units and communicates the request outcome(s) back to the interface.