49 and unlike the prior art can not be misled by a contamination of isolator 45 since such contamination cannot develop the modulating frequencies being processed by circuit 42 further electrical circuit 42 controls the fuel supply through fuel solenoid 41 accordingly should the flame be extinguished or alternately become too hot the fuel supply can be automatically modulated this automatic modulation occurs while simultaneously sending an alarm signal item 44 to operating personnel fig3 illustrates a detailed electrical schematic of one embodiment of the circuit 42 of the present invention which generally includes a power supply filtering means detection means and a frequency comparator by reference to fig3 a probe current exciter 60 is provided a stable voltage by power supply and filter 61 when the flame body 49 is not providing a connection between probe 34 and pilot body 30 the applied voltage will not result in current flowing through probe 34 should isolator 45 become dirty or wet it is expected that some current will begin to flow through probe 34 however this current will not be processed through the amplifier circuitry due to the direct current isolator 66 which is not adapted to process direct current even when the isolator 45 becomes wet or dirty when a flame 49 is present in chamber 67 the modulating impedance of the flowing ions will develop an alternating current signal which can be processed through direct current isolator 66 frequency and amplitude selective amplifier 68 is adapted to amplify and process the appropriate signals to a threshold detector and square.