1) Before loading a cone onto the cone supports, check that the actuating rod can lift up and down freely. If the rod movement feels sluggish, corrosion may have built up inside the tube. Sometimes you can clean out the tube using long cotton-tipped applicators. (They look like Q-Tips.) Do not fire the kiln until the actuating rod moves freely. If necessary, replace the tube.
2) The cone supports (the metal tabs where the small pyrometric cone is placed) must be clean. Use emery cloth to remove traces of greenware, corrosion, or bits of melted cones. These foreign materials will catch on the cone, preventing it from slumping freely. Coat only a small amount of kiln wash on the lower side of the rod and on the upper edges of the cone supports. A build-up of kiln wash will alter the cone's shut-off temperature.
3) If the Kiln Sitter does not shut off when the weight drops, the locking slide inside the Kiln Sitter may be corroded or dirty. About once a year, unplug the kiln and remove the switch box that houses the Kiln Sitter. Pull the box straight out to avoid damaging the Kiln Sitter tube. Leaving wires attached, clean the backside of the Kiln Sitter. Canned air is helpful. (But do not blow air into the Kiln Sitter tube.) When you reinstall the switch box, arrange the wires so they do not interfere with the locking slide that trips when the weight drops. (You can see how the locking slide works by lifting the weight, pressing the plunger, and then dropping the weight.) Also, arrange the wires inside the switch box so that wires do not touch element connectors or the kiln case.
4) Adjust the Kiln Sitter using the firing gauge. This is a small disk that ships with new kilns. (Many people throw away the firing gauge thinking that it is used only during shipping.) Adjust the Kiln Sitter with the firing gauge every dozen or so firings.
How to Use the Firing Gauge
Place the gauge on the cone supports, sliding the actuating rod through the hole in the gauge. If the actuating rod is not centered in the porcelain tube, loosen the two screws on the guide plate and move the guide plate from side to side.
Lift the Kiln Sitter weight to the raised position. With the firing gauge in place, the trigger should just barely clear the release claw, coming as close as possible without touching. If the gap is wrong, loosen the set screw in the center of the weight, move the trigger and retighten the set screw.
This adjustment is easier to understand when you see pictures. You can download the Kiln Sitter instruction manuals at Paragon's website. (Click on "Manuals.")
5) Never lean anything against the kiln's switch box. A shelf leaning against the Kiln Sitter can prevent the weight from dropping, causing an over-fire. Leaning something against the Kiln Sitter can also put it out of adjustment.