Abstract: An integrated circuit dc-comparator compares voltage signals representative of sump water and collector water temperatures in a solar energy conversion system and continuously provides a direct current voltage signal from the time that it is sensed that the collector water is 11.degree. F warmer than the sump water, until such time as it is sensed that the collector water is only 2.degree. F warmer than the sump water. The integrated circuit is latched to provide the continuous dc signal notwithstanding variations in noise level, by a resistor connected between the integrated circuit output terminal and the integrated circuit input terminal at which the collector water temperature is sensed.