A control for a water heater having upper and lower heating elements assures that the upper heating element is not activated until certain control conditions are met. The control first determines whether the temperature sensed by a sensor in the vicinity of the upper heating element has reached a predefined set point temperature for that sensor. The control thereafter determines whether the temperature sensed by the sensor declines at a rate greater or equal to a threshold rate of temperature change before authorizing any activation of the upper heating element.