The Original Prusa MK4/MK3.9 is showing the message: "Overcurrent detected on nozzle heater."
Error name: Nozzle Heater Overcurrent
Error code: #13308 (MK4) #21308 (MK3.9)
The error is shown when there is a damaged cable on the hotend heater or any of its connections.
The most likely cause of this issue is damage to the hotend heater cable. Check the path between the hotend heater and the LoveBoard, and see if there are any parts that are broken or pinched.
In case there is no damage, check the cable connection to the LoveBoard board. Try reconnecting the cable to its connector.
In rare cases, this error message can be shown in case of damage to the LoveBoard, or to the xBuddy board. So if the cables and connectors are intact, check the boards for any visible damage.