a control device for monitoring the presence or absence of a flame through the use of an ionization tube sensitive to radiation of a predetermined wavelength and which is emitted by the flame . energy storage means are employed to accumulate the signals generated by the ionization tube . the stored energy is periodically pulsed to discharge the stored energy in an intermittent manner thereby delaying the generation of a signal representing the absence of a flame . the state of the energy storage means is digitized at the aforesaid periodic rate and is restored generally to its undigitized form before controlling the delayed generation of a flame - out signal .