Assuming yor problem is not working on AC and you have a $6 Volt/ohm meter I'd do a couple simple tests. I'd first check that you have 115V at the outlet. Next I'd check for 115V on the pair of heavy wires that go to the flue. They come out of the bottom of the board to the left of center. If both tests have 115V then I'd do a ohm test on the electric heaters. Unplug the 115V cord from the outlet and using a needle nose pliers pull the two pairs of wires loose from the board. Using the lowest ohm setting check for continuity for each of the two heaters. Seems like you should get 50 ohms if I remember correctly and one burned out will stop it from working on AC.
PS: Be sure to turn the meter from ohms settings as the next time you are in a hurry to do a volt test you will get a burnt smell from the meter. I'm just glad they are only $6 now.
This may be the control board for your unit.