Z-axis not moving up

I am having a problem with my Vertex K8400 3D-printer for a while. Sometimes it just refuses to move it’s z-axis upwards. When I select control printer > move axis and then try to move the z-axis up, it moves downwards. When I try to move it downwards, it also goes downwards.
The same occurs when I try to start printing: when calibrating, it moves all the way down (where it normally moves up towards the nozzle) until it jams and I have to stop it.
This problem occured a few times earlier, but when I restarted and resetted it a few times, it would resolve itself. But now, even after restarting and resetting several times, it won’t go up.
Does anyone know this problem and/or have a solution for it?

Thanks in advance.

Kind regards,

Niels

This sounds like a dirty or defective end stop
Try cleaning it with a soft cloth.

Thanks. I just cleaned it, but I keep having the same problem.
I use Control Printer > Move Axis > 0.1mm > z-axis and try moving it upwards. When turning the button anti-clockwise, the z-axis moves down and the LCD-screen displays an increasing Z-coordinate. Moving it clockwise makes the z-axis move down as well, but the LCD-screen displays a decreasing Z-coordinate. When the Z-coordinate is all the way down to zero, the axis doesn’t move while turning the button clockwise. When turing anti-clockwise the process starts all over again.
I also deconnected the thread from the motor to make sure nothing is going on in the end-stop (because this will hold it from pressing the end-stop), but this gives the same result.

Do you have any other ideas what might be causing this problem to occur?

Thanks

Sorry it’s been so long.
If cleaning it didn’t help try swapping it to a different location to see if the problem moves with it