Originally Posted by Bama Rambler
So the furnace has never worked?
It could be a bad gas valve or a kinked gas line. Have you checked to make sure you're getting 12 volts to the valve solenoids when it's trying to fire?
This is good advice. Especially if the furnace is in a slide. There have been lots of reports of ovens, stoves and furnaces not working because the line was kinking as the slide moved. Happens in stationary positions as well.
These furnaces are not really complicated and the service manual has a real good troubleshooting guide. If you don't have the manual, they are available online.