HMMMM...... Where to start I wonder.It should work when plugged into 115 and propane is selected unless auto is left on. It should try to light 3 times and then lock the board out, requiring it to be reset. It will always default to electric when it is available. You should not have to unplug it. Good that it fired so you know it worked, now to find the problem with the 12v side that is not telling the board to use propane. The system uses 12vdc to work the controls, 115 ac only heats the elements.