One color missed, doesn't extrude

[bonsay_x]

Hi everyone, I recently purchased an A20T.
Since a few days a color has not been extruded, I have tried to invert the extruders, the PTFE tubes, but the clogged hole is always the same, even by rotating the hotend.
I measured the current of the heating cartridges, they are all ok 23.6V.
I tried to replace them but the problem remains.
the color is extruded only if the temperature is 250.
can anyone solve this problem?
Thank you all

[William]

Hi,if printing in monochrome, it is best to insert consumables to avoid blocking the nozzles due to backflow.