138 39 is connected to the base of transistor 146 39 capacitor 150 39 is connected between the emitter and base of transistor 138 39 while resistor 152 39 is connected between the collector of transistor 146 39 and the base of transistor 138 39 connected between the negative terminal of timing capacitor 124 39 and lockout actuator 30 39 is a network of diode 154 39 and resistors 156 39 and 158 39 diode 160 39 connects diode 154 39 to the base of transistor 116 39 darlington pair 110 39 is triggered into conduction by the turn off of transistor 116 39 circuitry for control of darlington pair 114 39 includes transistors 170 39 172 39 the collector of transistor 172 39 being connected via diode 174 39 to the control electrode of darlington pair 114 39 darlington pair 114 39 is triggered into conduction in response to a flame signal on bus 108 39 applied through voltage divider network of resistors 118 39 120 39 and 122 39 or conduction of transistor 146 39 unless its control electrode is clamped to ground by transistor 172 39 in conduction the base of transistor 172 39 is connected by resistor 176 39 to line 178 39 an unlatching network responsive to loss of signal on bus 108 39 includes resistor 180 39 coupling capacitor 182 39 and diode 184 39 and is.