Help with Peerless PF-140, Ignition issues, Control Board swap

If you can't get an adjustment out of the gas valve then the gas valve has failed. The blackened heat exchanger is a serious out of adjustment valve.

You can have your tech try and set up the old valve as if it's a new replacement valve. Turn the throttle adjustment screw, not the offset screw, counter clockwise which will completely close the gas valve. the throttle adjustment screw will have a plus and minus sign with an arrow stamped around it. After the throttle screw bottoms out, turn it back clockwise 6 full turns, paying very close attention to the number of turns. If the valve is good this will give you a starting point to get ignition and maintain a flame. From that point all have to do is tweak the throttle adjustment screw to get your combustion numbers where you want them. If you don't get flame or no change on the manometer at the test nipple on the gas valve then you gas valve is no good.