Last week my kiln's relay got stuck. Instead of firing to the temperature I had programmed (1250 F) it ramped all the way to 1675. Fortunately, I caught it and shut off the circuit breaker. The glass and ceramic mold were ruined, but it could have been more serious.
I contacted Paragon and they were able to help me diagnose the problem. Apparently, relays do get stuck on occasion. My kiln is several years old. In the newer models, they use a 2-relay system. Mine has only one.
I ordered the part and was able to install it following their online instructional video.
If you have some temperature variation, it could be the thermocouple. But in this case, the variation was more than 400 degrees. Another lesson in keeping an eye on your kiln!