I did some research the other day as Mike suggest on RV.net and I'm thinking had too many vents closed, thus not allowing the sail vent to open. I had two of the 4 registrars completely closed. 1 in the bunk area, we had no kids this past weekend, so I didn't worry about heating the bunk area, the other closed just under the thermostat. Opened all the registrars fired up the furnace the other day, let it run for 24hrs, no problems based on the min / max digital thermostat I placed in there.
Either way the unit is at the dealer for what appears to be the ends of the axle collapsing, and they said they would check out the furnace too.