Abstract: The systemizer control enclosure is provided in the form of a box having a top wall, a bottom wall, a left wall, a right wall, back wall and a front cover hinged to the right sidewall. An A.C. input power cord extends out of a cord connector mounted in the left wall. A sensor inlet opening is formed in the right wall for the sensor wiring. A.C. output power cords extend out of a plurality of strain-relief cord connectors in the bottom wall of the box for connection to the boilers, pumps or other heating system devices controlled by a typical boiler control unit. A component mounting plate is secured to an interior surface of the box. A boiler control unit, switching relays, a screw-down-terminal input/output wiring connector for connecting the wiring of the sensors to input terminals of the control unit the input and output power cords and a step-down transformer for supplying power to the boiler control unit and relays are pre-wired and mounted on the mounting plate.