My one year old Ruud # UGFD-10EZCMS 90% UP FLOW keeps throwing codes 13 and 12 and after a while it shows r. A service guy came over and said it was the flame sensor. He replaced it and not the problem. Then he replaced the circuit board. Not the problem. This company is now not interested in finding out what the problem is. It has cost me so far $206.00 to fix nothing. Anybody have any ideas as to what it could be?