Atwood Furnace 8531-IV-DCLP Only burns when igniter....

The board is likely not sensing that the burner ignited. The igniter tip also acts as the flame sensor and may be out of position or dirty. The first thing I always try though, is to remover the wiring connector at the igniter board, and reinsert it a few times to clean the contacts. The flame sensor provides just a tiny voltage, so even a small amount of corrosion can interfere with it. Worst case, the board has failed, in which case I recommend getting a Dinosaur brand board to replace it.