Can a digital kiln over-fire?

If the digital kiln gets too hot, the controller is designed to shut off the kiln. This is one reason so few digital kilns over-fire. Nevertheless, over-fires definitely happen. When a relay fails, it usually fails in the "off" position. If a relay sticks in the "on" position, the elements wired to that relay will remain powered even though the controller has shut off the kiln. On a small kiln with one relay, a stuck relay could result in an over-fire since all the elements will remain powered. On the larger kilns with two or three relays, a single stuck relay will keep the temperature at a mid-range. All kiln manufacturers warn not to leave a kiln unattended.