I started getting the following error in OctoPrint from my CR10S:
Offline (Error: MAXTEMP triggered, system stopped! Heater_ID: 0 - MAXTEMP triggered, system stopped! Heater_ID: bed)
Neither rebooting the printer nor the OctoPi cleared this condition. After trawling through many posts I stumbled on this one which had a throw-away comment about the SD card maybe being corrupted from user foosel:
Just a hunch. Eject the SD card that’s in the printer.
Sure enough after removing the SD card from the CR10S power box - it worked!