We have been putting these in some apartment buildings (per their spec),and I got a call yesterday for blowing cold instead of hot. Went over there and found the installer never set the jumper on the furnace board to "heat pump". I corrected that and verified good heat pump operation,and left. Today I get the call to go back because of no heat again. Found out that the problem happens at night,when it calls for aux heat. Furnace flashing red twelve times ("ID plug loose or not attached"). Can't find anything wrong. The ID plug is in place. Pulled all stat wires from board,powered up - flashes 12 times. I am assuming the board is bad at this point as I can find no external cause. Even reversed polarity and re-checked. I don't like these things. The gas valves are crap,and the pressure switch design begs for service calls. Anybody seen this code before on this furnace?