There are Atwood furnace troubleshooting guides available on the internet, admittedly they are rather hard to find. I found one for my model when I was having an issue, a few years ago.
If you give us your furnace model number, perhaps we can help further.
Atwood has an error light or two on the unit, and you can troubleshoot the unit by counting the number of flashes during the failure. Sorry to be so vague, but troubleshooting is model specific.
There is also a section on the forum where you can get manuals for various RV devices, I will post the Atwood 8500 series if it's not there.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4