Gas Furnace and Flame sensor aka flame rod is a part of a flame proving system. the flame burns across the flame sensor and to the heat exchanger. the flame conducts electricity and clears the circuit, the flame acts as a switch. the flame rectifies the alternating AC current to a pulsating DC current that the control board can read. the flame doses not conduct electricity very well so the amperage is very small or micro. we read it as micro amps with our meter. #love2hvac #hvactechnician #hvaca