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Check Z-probe trigger position
To deploy the Z-probe, the effector moves to the deployment position, then travels across in the -X direction so that the short leg of the probe snags on the Z-timing-belt and is flicked over until it can be pulled down by the spring.

Test it by homing the printhead (G28), then send G29 to deploy the Z-probe, with one hand on the power switch or cable. If it fails to deploy as it passes the Z-timing-belt, power down at once, disconnect in Pronterface and follow the troubleshooting paragraph below.
You can lengthen the arm slightly if necessary with a small piece of 1.6mm heat shrink tubing (supplied). It is a good idea to fit this anyway to avoid possible long-term wear on the belt by repeated triggering of the probe.
Troubleshooting
If the Z probe fails to trigger on the belt, you need to adjust the starting position in Marlin. The relevant settings are in the Marlin_main.cpp file under void deploy_z_probe() on line 826, about a third of the way down this very long file. A couple of lines below it the positions are given as:
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So if the trigger needs to move close to the belt by 5mm add 5 to the number after “destination[Y-AXIS]” (in this example 95 would be increased to 100.
If the belt needs to start or stop further left or right of the belt the adjust the Two “destination[X_AXIS]” numbers, the first is the start position, the second the end position.
Set and test Z-probe retract position
After probing the print-bed levels at a grid of positions, the probe is moved to the retract position and lowered until it hits the capscrew and/or M3x12 penny washer which pushes it up until retracted.

We have set the probe retract position in Marlin so that it it should work when the target is at 82mm from the left-hand end of the X-Z extrusion, so check this before proceeding with this test.

Once the probe is deploying correctly, allow it to run through the whole probing sequence and attempt to retract itself. Whether it retracts or not, it will park itself above the retract position set in Marlin.

If the position needs adjusting, then use Pronterface to move the probe exactly over the centre of the retract-bolt, lower it until it just touches, and then send M114 and make a note of the coordinates reported. The retract position is in the Marlin_main.cpp file - find void retract_z_probe() on line 839, and a few lines below it the positions are given as:
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Change the X and Y values (ONLY) of the destinations to the values you have just determined, save, upload and test. Note do not change the Z positions to the results you got using M114 or else the probe will crash into the bed and retract tower.
Set Z-Probe offsets
The distance between the tip of the Z-probe and the tip of the hot-end needs to be set accurately. The offsets are defined in Marlin configuration.h, around line 355:

The first number ( 0 in the above screenshot) is the X-offset - normally close to zero as the probe is directly behind the hot-end.
The second number (13 in the above screenshot) is the Y-offset: the distance between tips in the Y direction.
The third number, the Z-offset, is critical and will be measured and set as below, following Johann Rocholl’s procedure at [github.com] (bottom of the Readme).
Place a piece of the supplied blue tape on the Printbed near the centre. Make a small cross-mark on the tape with a marker/felt-tip pen near the centre of the bed.
Move the tip of the hot-end in Pronterface to position it exactly on the mark and touching the bed (Z=0), then move the nozzle up 0.1mm using Pronterface.
Display this position by sending M114:
>>>M114
SENDING:M114
X:-0.60Y:0.90Z:0.80
This will be “Nozzle Zero” position
Raise the hot-end by 20mm to ensure there is clearance for the probe.
Manually trigger the Z-probe and use Pronterface to place it directly over and almost touching the mark on the print-bed.
Lower the probe 0.1mm at a time until you hear the click of the microswitch as it is released. If you can’t hear it, send M119 in Pronterface after every 0.1mm to check when the Z-min endstop triggers.

Before triggering, left, and after triggering, right
Now send M114 in Pronterface to get the position of the probe, which gives the offset values.

Record these values as “Probe Zero” and subtract the “Nozzle Zero” positions from them. Eg for the values shown above:
Probe Zero Values - Nozzle Zero Values:
X:2.90Y:-17.00Z:3.60 - X:-0.60Y:0.90Z:0.80 equals
X:3.50Y:-17.90Z:2.80
and enter them in the define Z_PROBE_OFFSET field in Marlin, changing the signs:
#define Z_PROBE_OFFSET{-3.5,17.90,-2.8, 0}
Now disconnect in Pronterface, re-upload Marlin, reconnect in Pronterface, set the extruder temperature to 185C, home the printer (G28), and then probe the bed (G29).
Enter G1 X0 Y0 Z10, then use Pronterface to move the hotend towards the bed, using a piece of paper as a feeler gauge. The paper should just drag when the hotend reaches 0 on Z (use M114 to confirm)
Troubleshooting:
If the hot-end reaches zero before dragging on the paper then the Z value of the offset in Marlin is too little, so increase it by the estimated amount plus a mm more and repeat until you have the correct setting.
Repeat the home/probe/measure sequence until there is no further error between the probe height and the measured height with the feeler gauge.
Finally, home the printer, which removes the Z-height determined by the auto-levelling process and resets the Z-height to the MANUAL_Z_HOME_POS value. Send G1 X0 Y0 Z5 and lower the tip onto the paper again. Exactly the same amount of drag as in the original Z-height measurement means you have now exactly measured the offset.
Check the range of X and Y travel
This is a check to ensure the printhead can move around the extent of the printbed when close to the surface without snagging on anything.
Move the printhead to 1mm off the bed (G1 X0 Y0 Z1).
Move to:
G1 X85 Y0
G1 X-85 Y0
G1 X0 Y85
G1 X0 Y-85
simply move to X=85 and -85 with Y=0,
and to Y=85 and -85 with X=0, using the G1 command with the appropriate coordinates. Check visually that the hot-end tip is about 5mm from the edge of the 180mm mirror glass printbed. Finally home the printer.
IMPORTANT NOTE: Don’t try moving the printhead in the X and Y direction when it is homed. One or more of the carriages will try and move upwards past the endstops and will not respond to endstop triggering. This could damage the motors, belts and electronics. Always move the printhead down in Z at least 100mm before moving in X and Y.