I don't know if it would be the board or not. Why would it work ok in June and then not in Oct? When was the grill mod done?
ISTR the igniter probes work better when they are hot, from a trick you do with a lighter when trying to get a pilot flame to stay lit.
I wonder if your igniter would work after you light it with your lighter, let it burn for a couple minutes, then turn it off with the switch inside that has the red light. Wait a minute then try the switch and see if it works now. If so, that might mean the board is ok?
What was going wrong with the first heater? Same thing as this? If so, something else is happening somewhere.
We need Doug R to save us here!