As Dave said there are several things that need to be considered, we need complete information and if possible a few pics of the installation:
Is the stove Power vented or direct vented, if so how are you controlling the draft?
What kind of interlocks does the stove have, flue switch, thermal disc, etc?
Does it have a barometric damper and if so how did you adjust it?
Did you set up the idle for minimum fire, if not it will be different depending on whether you are using the coal-trol or Alaska control?
How long did the stove operate before this problem occurred?
Have you tried removing the coal and just plugging the stoker motor into a wall outlet to see if it quits with no load?
The more information we have the quicker the problem can be found.