Abstract: A programmed controller for controlling the start of a heating system includes a clock mechanism to produce a time-variable signal, two temperature transducers, one inside and one outside of the building, and an electronic circuit which is a proportional summing means to combine (in predetermined proportions) the electrical outputs of the two transducers, and an electronic circuit to combine the time variable signal with the summed transducer output signals to thereby produce a control signal for controlling a heating appliance, such as a boiler.