Geeetech

Hello,
because every time I turn off the printer, when I turn it on again I have to level the bed.
Once the bed has been leveled by a further check, the distance from the nuzzle to the bed changes at different points on the bed.
Why?
I do not know what to do anymore, what could be that it does not work, the plate where the bearings are fixed or the heating bed or maybe the glass could affect.
If I replace the glass bed with an aluminum one, I solve the problem?
Thank you

I think the issue may the Z axis rod
Could you tell us your printer model?

I hawe a Geeetech i3 Pro C

You can send G28 Gcode ,Mark the left and the right of the X axis
Then control Z axis via LCD and then up it to the top
Send G28 Gcode again
Then you can record the height right and left of X axis
Last,you can ensure the issue root is the rod or not