I've given up with the BLTouch and am now using a capacitive sensor instead. It works remarkably well, detecting the print surface about 4mm away.
Whilst I had tried to use a capacitive sensor previously, that had failed due to it needing to touch tyhe print surace before making the detection. I have since discovered that was due to the capacitive sensor being driven with a low 5v supply. When I changed that to 24v it started working as required.
Whilst I had tried to use a capacitive sensor previously, that had failed due to it needing to touch tyhe print surace before making the detection. I have since discovered that was due to the capacitive sensor being driven with a low 5v supply. When I changed that to 24v it started working as required.