Furnace won't light.

I have a Rockwood 2905ss. Has a Domitec furnace. Last year one night one of my propane tanks ran empty and it automatically switched over like it should. Problem is ever since then I can't get my furnace to light. It tries but stops after 30sec or so. What am I doing wrong?


Ontario, Canada
2014 Ram 1500
2015 Rockwood Ultralite 2905ss