For any of those that work on rapid air systems. I normally do not work on these and have come across a problem I can only guess at. I have a MAU system w/ 6 or 7 burners. Cust. says they shut it down due to it producing 50 ppm intermitantly. They have not seen what the burners were doing while it had this problem. I looked at it and cycled the thing at least 30 times in high and low fire. I can only get it to produce about 9 to 15ppm and the burners light fine. It has 2 honeywell fluid valves, a maxitrol high and low fire gas valve, and air stream switch, variable dampers, and a pilot valve. I have plenty of gas going to the unit and 2" on high fire. Only thing I can come up with is that this unit is an a area where semi's pull in and out of on a somewhat regular basis and the intake for it is right out side a roll up door which the unit is right on the other side. Maybe it is pulling in exhaust? What are your thoughts on it? Thanks.