An improved system and method for controlling the temperature of a resistance heater in a heating, ventilation and air-conditioning (“HVAC”) system is disclosed. The control circuit and method includes three separate thermostats per heater leg and are designed to trip at three, sequential pre-selected temperatures to address certain issues associated with prior art designs for thermal overload protection. One of the thermostats is of an automatically resettable type wherein the remaining two are of a “one-shot” design and will remain open until there is human intervention.