Abstract: A control system is disclosed which comprises a first control module generally integrated into a controlling device (e.g. a thermostat), and a second control module generally integrated into an electrical apparatus (e.g. a heating apparatus) under the control of the controlling device. The second control module is responsive to command signals remotely transmitted thereto by the first control module over the power lines which power the electrical apparatus. In response to the signals, the second control module can selectively turn on, or off, or modulate, some or all of the electrical components (e.g. heating elements, fans) of the electrical apparatus.