An improved spa control system is disclosed. The improvements may be made individually or in conjunction with any combination of all of the other improvements of the present invention. The invention describes a spa control system which calculates the rate of heating of the heater of the water in the spa to control the operation of the heating element. The system uses a interconnection panel to link a control panel to the power supply and to the operative components of the system. The unique connection of the control panel to the interconnection panel permits the control panel to be located adjacent to the spa.