upps... what happens is that the control box puts out 12V on the flamse sensor, the sensor is just a photo transistor that sits at the end of a tube that sits in the flame, so when there is a flame after 10 seks or so it will be very bright inside that tube and the voltage will drop to arround 1V
my guess is that the optocoubler i use at the input actually pulls those 12V to ground hence makes the heater think there is a flame before there should and that makes the heater shut down at once...
not that i'm a total noob but what would the best way be to sense those 12V without making the voltage change to much?