The furnace will usually time out and turn off the fan if it doesn't sense the burner firing. If the burner is not lit (you should be able to hear it) and the fan continues to run then you have a controller problem. Maybe it's wet? Common Thor problem.
Just some info. The ace we had the furnace would not lite. Found out that if you close the regulator. Then ever so slowly turn the regulator on (at the tank) I'm talking real slowly so not to cause any surge to the line. Then lite kitchen burner first to remove any air. Then try furnace. Was the only way our furnace would lite in the ace. Maybe worth a try
update on no heat blowing cold air after one cycle of heat.
Dealership found that the control board is defective and the ignitor is bad.
replaced at no cost, under warranty.
thanks to everyone that helped.