I made a few successful prints since I got my CR-10 two weeks ago and I didn't run into any major trouble. The printer is new.
Today I set it to "preheat" mode while I was preparing the SD card with the settings being 210°C for the nozzle and 60°C for the bed. When I wanted to start the print I noticed that the temperature showed as "actual temperature" on the printer's screen showed 233°C and it was going up steadily while the "requested" temperature was still 210°C.
Thiking it might be a mis-manipulation on my part I powered it down for a few minutes (I got scared by the high-temp) and then powered it back on. I then immediately requested the print to start. The CR-10 heated up to the proper value, started printing and kept heating the nozzle. I stopped it at 217°C.
I looked for an answer on the internet but all I could find is people having trouble with the nozzle not heating at all ...