The temperature values in the touchscreen fluctuate when the machine is working.
1, Please cool down the nozzle and the heated bed, then check the temperature values on the touchscreen.
Normally, the temperature values are close to the room temperature. If the temperature values are far away from room temperature, the thermistor is defective. If the temperature values are close to the room temperature and fluctuate in a small range, the thermistor is unbroken.
We offer a new backup one in the package, please find it by referring to the quick start guide.
Please refer to the following video and the images to replace the hot end.
After the replacement, you can power on the machine and heat up the heated bed again.