IR probe offset fluctuates

[StuartMoorhouse]

Ive got a kossel mini with a duet running firmware: 1.10+4 (2016-03-30) and a DC42 IR probe.
Recently Ive had a few problems calibrating, the issue is that the Z probe height offset seems to vary.
So far i've:
Heated the bed and extruder to PLA temperatures.
Homed the printer
Brought the nozzle down to the print bed using a piece of paper to determine where Z=0.08mm and set Z to that height
Lifted the nozzle 5mm
Run G30 s-1
Read off the head position as Z=1.09 and updated the relevant section in the configuration file.
Run G32

Then when I bring the nozzle back down to the bed, I can take it all the way to Z=0 and there still be a slight gap between the nozzle and the bed.

Interestingly I noticed when bringing the nozzle down to the bed the IR probe is triggering at Z=1.30
If I repeat the above process again running G30 s-1 now gives me a Z height of 1.27mm.

Has anyone had any experience of this or is there something i'm overlooking?

The level of ambient light isn't changing and the z probe board is firmly attached to the Effector assembly.

Thanks
Stuart

[Pumlux]

Are you sure your mount for the z-probe is thight enough to reproduce the height exactly ?

When I used a printed mount for my z-probe with a clamp in fixing, my height also was changing.
After using a metal mount system with having the z-probe screwed to it, the height is realy reproducable .
You already mention you have variances in about only some 1/100 mm.
The remaining factors are heat elongoation and the bad results when I hit the bed with the nozzle for some reason.