The printer is showing the error "Check the heatbed thermistor wiring for possible damage."
Error name: Bed Maxtemp error
Error code: #13205 (MK4) #21205 (MK3.9)
The error happens when the printer's heatbed temperature goes above 125 ºC at any point. This is a safety feature to prevent printer damage. In this case, the printer will stop the heating and display the message on the screen.
Make sure that the ambient temperature where the printer is is stable, and above 10 ºC.
This error is usually caused by a damaged heatbed thermistor.
Check if the thermistor is well secured under the golden Kapton tape.
In order to test if the thermistor is damaged, go to the printer menu in Settings -> Temperature -> Heatbed temperature, and set it to 80 ºC. Then, move the heabed cables by hand and see if the temperature will fluctuate. If the temperature fluctuates more than 5 ºC, from the set temperature, the thermistor needs to be replaced.
Open the xBuddyBox-cover and the el-box-cover by opening the screws indicated below to access the heatbed cable connectors. Make sure that the heatbed power cable did not slip from the screw, and that the heatbed thermistor cable is well connected.
If you have a multimeter, you can check the resistance of the cables using this guide: Multimeter usage