Thanks for the resply, Freon.
I've discovered something rather interesting. I went into the attic just a few minutes ago to watch the flames after the heat came on. The louvered cover has been off for a couple of days and I've been running the heat intermittently. I don't run it at night because of my fear of a fire.
Anyway, I put the louvered cover back on and the flames immediately crept out to the sides of the holes in the heat exchanger. So, I removed it, again.
I've owned this house for 3 years, and this is the first time I've had trouble with the heat. I've been putting the cover back on the way it came off each time. The reason I know I've put it back on the same way is because there's a sticker on the top of it that has the name of a local HVAC company.
Anyway, just for the heck of it, I tried rotating the cover 180 degrees and putting it back on. Well, guess what....the flames are staying confined to the holes in the heat exchanger. There is no flame creeping out the sides now. The only difference is that the louvers are angled opposite of what they were before. The HVAC company's sticker is now upside down and at the bottom.
So, does this make any sense. Does the direction of the louvers make a difference. The louvered cover has been in the other position for at least 3 years.