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.