Cause investigation: No wiring of tool head or thermistor failure;
Solution: Shut down and replug the toolhead cable and thermistor, and restart the machine to confirm the issue. If there is an error in preheating after restart, it indicates that the thermistor has been damaged and needs to be replaced. This step needs to disassemble the tool head. Check the website link for the disassembly process, Watch it from 3:19 minute.