Overfiring Keystoker

purchased home with a koker furnace. works fine for the most part but occasionally overfires into the 650 700 degree range once was buried to 900. glass cracked, don't know if this was the culprit. is the overfiring simply a function of controlling the draft in the flue of something else? would like to be able to relax and not check the thing every 10 minutes this winter. any help is much appreciated

If it's over-firing your fire is getting to much air or coal. Someone familiar with stokers can be more help but it sounds like a dangerous situation so I would shut down until you find out why. (make sure you have working fire/CO alarms too)

Where are you measuring the temp? On The stove itself? Front, Sides? The exhaust?

The stoker adjustments may be adjusted too far and it's burning off the grate? Can you check the burning on the grate at full burn to see how much is burning? Should be about 1" of ash on a full burn.

Also, do you have a standard chimney, (Brick, metal? How high?), direct vent, power vent, baro damper, etc....? How is it setup.

measuring temp right in front on the stove above the door. never burning off the grate but it does get close to the edge. vents into masonry chimneyclosed down the damper(Baro) and it helped some but it's stabilized at about 600f. wonder if my thermo is bad. took the two off the hot air pipes and they're a little lower temp