Printing problem

I know it's a pretty generic title but here's the problem.The print starts then almost immediately the printer adds .19mm to the Z height. this causes obvious problems. I have two almost identical printers . One does this, the does not. I figure that elinminates something odd in the G code at I think so I admit to not have read it yet. G code was generated with Cura and slic3r and there is no difference to the problem between the two with identical STLs. I tried re-flashing the firmware to the printer (Marlin). Then tried up-grading the firmware.It all worked OK but the problem remains. I seem to be able to send a G92 Z0 command after the print starts and the z axis shows 0 again. This is according to the LCD monitor on the printer. The layer height is set at .2 so a .19 increment is especaily odd. anyone have any ideas?

Hi Oatridge,

oatridge Wrote:
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The print starts then almost immediately
> the printer adds .19mm to the Z height.

When exactly does it add the extra? I'm sure you're aware that as soon as the Z axis homes, it will lift slightly again (according to the layer height set) just prior to the X,Y moving to the centre. In effect, it adds the layer height set in Slicr3 to the Z=0 (0.1mm?) height. At least, that's the way I see it!
So is it lifting again after it reaches the bed centre or something?

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Waitaki 3D Printer