We have the above model number furnace. We leave the fan on when we are home. We have been noticing that for the last couple of weeks or so, the temperature that our thermostat is set at is not being attained by our furnace. The fan will be running but the furnace will not be. When the lower access panel is removed from the furnace and immediately replaced, the furnace kicks on and begins heating again. This problem has been occuring a couple of times a day. When the furnace is not running and I have not removed the lower panel to restart it, the LED light flashes red 4 times, (which the panel tells me is a limit switch open). When I have the lower panel off, the red LED flashes 9 times (ground line or polarity fault). When I put the panel on and the furnace starts, I get a slow amber LED flash (normal operation with call for heat). Please help! It has been below zero during the day and well below at night here in Minnesota, we need our heat! Thanks, Dan