I got to looking and on my furnace the fire seems to be coming from the middle of the pot all the time and from about half way down the pot. But my boiler the fire is all coming up around the edge of the pot and is barely burning in the middle. It looks like the the fire comes rom near the bottom

You and I seem to have the same issue........I cannot get adequate combustion temps due to the same buildup around the sides of the firepot.

It doesn't make the fire go out, just limits the output. My door temps are barely 250* if I leave it to run on its own. If I remove that buildup every 3-4 hours I can get 350* at the door.

Does your buildup look like this?

Could be similar, but corn will melt into a rock hard white clinker where the air can't get through for combustion. when you increase your air intake, will it burn a little lower in the pot? The clinker you seem to be getting is a carbon buildup from incomplete combustion. A little corn will alleviate most of this problem!