The Steca model TR 0301 U differential temperature control provides automatic, safe and reliable operation of domestic solar water heating systems. The TR 0301 U output is wired to a pump that circulates the heat transfer fluid between the solar thermal collectors and the storage tank during the course of the day. This microprocessor-based TR 0301 U utilizes two RTD (resistance temperature detector) type sensors to monitor collector and tank temperatures with digital accuracy. The LCD gives the homeowner a variety of real time information including system temperatures at up to three separate locations. The consistent use of simple pictograms ensures ease of operation and troubleshooting. In addition to the primary function of turning the circulating pump on and off during the day, the TR 0301 U provides important diagnostic and safety functions. For example, the LCD pictograms will indicate fault conditions such as sensor shorts or pump failures. The installation manual also clearly describes the fault symptoms, possible causes and remedies.