Digital kilns use a thermocouple to measure the temperature inside the kiln. The thermocouple is the small rod protruding into the firing chamber.
Bumping the thermocouple can push it out of the firing chamber. This could cause an overfire. The controller does not contain an alarm to detect this type of failure. Bumping the thermocouple could also cause it to give inaccurate readings.
Thermocouples come in different widths. The wider the thermocouple, the farther it should extend into the firing chamber. A ½" - ¼" diameter thermocouple should extend into the firing chamber about 1". A 1/8" thermocouple should extend into the chamber 1/2" - 5/8". (Do not be concerned if your thermocouple extends into the firing chamber even farther.)
Keep shelves, posts and ware 1" - 1 1/2" away from the thermocouple. If these items are too close, they can temporarily throw the temperature reading off. Keep an extra thermocouple on hand, especially if you fire hotter than 2000°F/1093°C.