The present invention relates to a control system for establishing and maintaining a desired uniform temperature in a room heated by a heating device. The control system includes a valve assembly for controlling the pressure of the fluid supplied to the heating device, the valve assembly including a valve actuator, a pressure sensor sensing the pressure of the fluid supplied to the heater, and a temperature control device to sense the ambient temperature of the room. The control system also includes an electronic control unit connected to the aforementioned elements, the electronic control unit including an electronic circuit which samples “open” and “close” input signals from the temperature control device, determines the rate of change of the pressure of the fluid from a predetermined pressure set point, and varies the pressure set point (which thereby varies the heating device output), according to the “open” or “close” signals by providing a command signal to the valve actuator. This command signal is based upon a difference between the predetermined desired temperature and the actual temperature, and the rate of change of the pressure of the fluid.