a well bore fluid is being heated to prevent paraffin build - up in the production line by an electrical heating element lowered into a pre - determined subterranean location . the heating element is controlled by a control unit that is connected to a temperature sensor , which detects temperature in the vicinity of the heating element and energizes an above - the - surface electric power source to deliver sufficient electric power to the electric heating element to keep the paraffin substance in a liquefied state .