I have a Coleman furnace DGAT070BDD . I am getting five flashing code . The minute the fan blows the fire goes out and continues to blow cold air. this is crazy, I replaced the board both upper and lower limit switches , gas valve, the blower, thermostat, the recalled heat exchanger and I am sure I am forgetting something . . I have spent almost a $1000. dollars and still it does not work. I am now out of funds and don't know what to do .