The PC705-2 is a microprocessor-based PID control designed to regulate the supply water tempera-ture to a heating system by controlling a boiler and the speed of an injection pump. The PC705-2 controls the system supply water temperature based on the outdoor air temperature (outdoor reset). A boiler sensor can be connected in order to prevent corrosion in the boiler due to flue gas condensa-tion. If the PC705-2 is controlling the boiler supply water temperature, the control continuously adjusts the boiler differential in order to optimize the firing cycles of the boiler, prevent large water temperature swings, and increase the efficiency of the system. A wiring harness is provided to be easily connected to the Taco Expandable (-EXP) Controls.