Auto-levelling and Z-endstop problem

I am stumped and hope that someone can help please.

I have changed the X-carriage and extruders on my Prusa i3 steel derivative printer and have added Z-probe capabilities using one of David Crockers optical boards connected to the X-max endstop channel. It works when I test it with a G30 P0 command, doing the three checks and then providing a response.

I also have Z-endstops on maximum and minimum channels. I have set the Z-probe offset (2.5mm) and the heatbed has three manual height adjustment screws.

I am using Repetier firmware (0.92.9), host (2.0.1) and server (0.80.3).

I have run through this page https://www.repetier.com/documentation/repetier-firmware/z-probing/ and think I have done everything correctly.

Symptoms:


1. When I home the Z axis with no Z-probing, the endstop triggers and the nozzles is about where it should be to print but the nozzles then raise a few millimetres. If I start a print it prints those same few millimetres above the bed

2. When I do a G30 P0 it works fine and returns results that make sense for the Z axis

3. Executing a G29 when the head is at the centre of the heatbed causes the Z-height to decrease to about 10mm then the X-axis goes to home and the Y axis goes to maximum (my Y-home is minimum) followed by a critical error reported by Repetier Host (G29 fialed, clear problem then run M999). Why does it try to home on Y Max, not Min and why does it error on G29?

4. G32 causes the Y axis to go to minimum again, the X to home and the Z to go to maximum where it hits the endstop and I get the error message from Repetier again.

What am I doing wrong, please?

Thanks.

Richard