| 431 / | HD | COMBUSTION |
| 18 | DF | TIMER, PROGRAMMER, RETARDER OR CONDITION RESPONSIVE CONTROL {26} |
| 42 | DF | .~ Sensor of first burner controls second burner, e.g., pilot and main, etc. {8} |
| 51 | DF | .~.~ Both burners cut off upon sensed extinguishment of first burner {2} |
| 52 | DF | .~.~.~ First burner manual reset valve cut off {2} |
| 55 | | .~.~.~.~ Burners independently controlled by reset valves |