Atwood 8525 IV Furnace - No Blower Run

Here is a link to the service manual that appears to cover your model. It has very detailed information and you should have no issue tracking it down. In general the first thing that happens after the demand for heat, is that the blower starts. You should be able to short out the terminals where the thermostat connects to the board. If that fails, and as you said you already replaced the board, I would suspect some type of connection issue.

http://bryantrv.com/docs2/docs/hflamefurn04.pdf