A water heater including a tank having a wall with an external surface and an internal surface defining an interior, and a circuit board mounted to the external surface of the tank. The circuit board including a thermal path for conducting heat through the circuit board, where the thermal path of the circuit board is thermally coupled to the external surface of the tank. An electronic switch is mounted to the circuit board and electronically coupled to a heating element, where the electronic switch is thermally coupled to the thermal path of the circuit board so that heat generated by the electronic switch is transferred along the thermal path. A temperature sensor is thermally coupled to the circuit board to sense a temperature of the thermal path relating to a temperature of the electronic switch and relating to a temperature of water stored in the tank.