A control system for bathers includes an electronic controller which controls operation of an electric heater assembly connected in a water flow path for heating water. The heater assembly includes a heater housing and electric heater element. A solid state water temperature sensor apparatus provides electrical temperature signals to the controller indicative of water temperature at separated first and second locations on or within the heater housing. The presence of water in the heater housing is detected electronically, by turning on the heater, and monitoring the temperature sensors for unusual temperature rises or other faults for a period of time thereafter. A solid state water presence sensor apparatus can also be used to determine the presence of water within the heater housing, providing electrical water presence signals to the controller indicative of the presence or absence of a body of water within the heater housing. An independent circuit apparatus is connected to the water temperature sensor apparatus and to a power relay, automatically causing high voltage power to be disconnected from the heater assembly when the water temperature exceeds a predetermined temperature. The independent circuit apparatus requiring a manual reset once the water temperature has dropped below a predetermined level to allow the high voltage power to be reconnected to the heater assembly. The system includes ground continuity detection, ground current detection and ground fault detection circuits.