Hi Nellie, welcome to the forum, Since you are running a Prill, I assume you are out in Montana, Wyoming or the Dakotas ??
Fill in your signature with your location, as Freetown Fred says: nobody will steal ya!!
IF the wiring and control box [is this the aquastat? give us a part number] then there is a reason that the boiler isn't getting too hot.
have you cleaned out the fines under the burn pot daily/weekly?? If the fines are clogging the combustion air holes, then you won't get much heat from the coal and the auger will run and run, pumpong unburnt or partially burnt coa out.
You mentioned the auger running , but you didnt' mention if the fire is burning at 100%, is there ash and clinkers falling off the edges of the fire? or is it unburnt raw coal??
The auger in most stoker boilers will run as long as the water is not hot enough, So have you checked to see if the inside of the boiler is all clogged with soot? have you cleaned the boiler inside lately?? Checked the chimney flue for soot buildup?
Just fishing fr more info so we can help