I'm thinking maybe the actual furnace isn't running, but possibly just the blower fan is running. Possibly the thermostat switch on the fire box is defective and telling the furnace the firebox is hot and needs the fan to cool it off, just like when the furnace turns off but the fan continues to run for a bit after the flame turns off. Might be a problem on the circuit board too. This is the link for the troubleshooting guide on the this site:
https://www.montanaowners.com/forums...?do=file&id=11