Geeetech

Hi,Are you referring to hot end automatic heating?
You can try to unplug the hot end line from the motherboard.

If the hot-end temperature is displayed as -14, the motherboard should have no problem.
Try to measure the thermistor at the hot end.

If the remaining temperature is displayed, there may be a problem with the motherboard.

I hope this can help you.

-14°C is "thermistor not connected" error.
999°C is "thermistor short circuit" error.

Geeetech, please use some contact conservation spray applied to contacts before packaging. Bad contact by oxidation is relative often case. I think that more pieces of silicagel did not help. Before cca 50 years was used special brown paper sheet with some chemical additives to make conservation microclima inside boxed electronics. Look for that with similar function.