hot end of 3d printer problem?

Hello instructors
 i build big 3d printer 1000mm *800 mm *800mm  its working ok . but i have problem with hot end in the second layer stop milting filament  i build three 3d printers but this the first time i see like this problem if any one have ideas what the solution 

thanks to u

Picture of hot end of 3d printer problem?
iceng1 month ago

And finally you may be feeding the fiber too fast and higher up it cools faster..

seandogue1 month ago

if it stopped heating sufficiently to melt the fiber, then either the heater element has failed, the wiring to the heater has failed, the FET delivering current to the heater has failed, the temperature sensor has failed, or the code isn't doing its job. Check each to isolate the issue, starting with the electrical properties.

براءا (author)  seandogue1 month ago

thank you very mach seandogue i check it before it not the mine problem to day i faind it s extruder problem didnot make the filament flow