Thanks Peter, restore the wiring to the high limit switch exactly as it was before, then set it down as low as it will go as a TEST...
the boiler should not attempt to fire with the high limit set below the temperature of the water in the boiler.....
then set the high limit switch to 175F and the boiler should fire. That is a critical test of your boilers high limit safety switch. We need to make 100% sure that it is wired correctly and functioning.
Do this heat stress test on the printed circuit board
Use a hair drier to slowly warm the printed circuit card up to120F or a bit warmer, but not over 140F... if there is any change in the error codes or other furnace behavior... the card has a cracked micro circuit that opens and closes as the card expands and contracts... that proves a bad printed circuit card.
No change however does not prove the card is good however... but a change proves the card is definitely bad.
When you refer to 'digits on the PCB' do you mean the tiny white dip switches? If so, they do not stick, but they can be stiff at times the appearance of being stuck would not indicate a bad PCB.
None the less, PCB failure is common. Use a magnifying glass and look for burnt or corroded or copper oxide spots (green corrosion) on the PCB.. if you see any of that, the board is quite possibly bad.
If you can use the paper clip icon at the right end of the tool bar, or the attach files link to the left of your send button to send me a close up of the 'stuck digits' I can be more explicit.
also, let me know how the heat stress test goes.