The actuating rod in the Kiln Sitter rests on top of the cone. As the cone bends, the rod moves downward and releases a trigger that shuts off the kiln.
As the rod corrodes, it no longer moves freely inside the porcelain tube. The rod’s pivot point causes sluggish movement of the rod. If your Kiln Sitter is giving inconsistent results, this is one of the possible causes. When you raise the rod from inside the kiln and let go, the rod should drop freely.
The tip of the rod corrodes as it ages. That is natural. However, if the corrosion extends all the way up to the pivot point inside the porcelain tube, your kiln is most likely subjected to too much moisture.
The solution to excessive moisture inside the kiln is to dry the ware longer before firing. You could also leave the kiln on low for a longer period at the beginning of the firing. It is better, though, to dry the ware thoroughly before placing it inside the kiln.
Leave the top peephole plug out. This allows moisture to exit the kiln through the peephole instead of through the Kiln Sitter tube. But if you use the Orton down-draft KilnVent, keep all peephole plugs inserted throughout the firing. Leave the KilnVent on during both firing and cooling. If you turn the KilnVent off when the kiln fires to maturity, moisture can build up inside the Kiln Sitter tube as the kiln cools.
If the Kiln Sitter tube corrodes even though you use a KilnVent, make sure that you have enough negative pressure inside the kiln. Orton recommends holding a match above one of the air intake holes in the lid. The air flowing into the hole should pull the flame toward the hole.