tube portion 14 is electrically grounded and serves as a third electrode flame rod 48 is designed to be much smaller than tube portion 14 and when no flame is present is electrically isolated from tube portion 14 of the housing 12 and hence from ground accordingly if no flame is present then no current will flow from flame rod 48 to tube portion 14 if the spark generated at second end 33 of spark rod 31 creates a flame flame rod 48 is positioned to be in the flame in other words the flame rod 48 is positioned so that the flame 50 will bridge the gap 51 so that spark rod 31 is no longer electrically isolated from tube portion 14 and a rectified current similar to that illustrated in fig7 is established that flows from flame rod 48 to tube portion 14 detection circuit 60 sends a signal to controller 62 based on the establishment of a current between flame rod 48 and tube portion 14 when a rectified current is established detection circuit 60 sends a signal to controller 62 in response to the signal controller 62 opens switch 76 to shutdown exciter 58 and hence stop spark rod 31 from generating sparks if controller 62 does not receive the signal that a rectified current is established within a predetermined period of time the timeout period then controller 62 will shutdown exciter 58 and stop fuel introduction into pipe 18 additionally in the case of a short or ground failure an alternating current can be established between flame rod 48 and tube portion 14 similar to the current illustrated in fig8 if detection circuit 60 detects an alternating current flow between.