Cannot calibrate printer  

Cannot calibrate printer

Hi,

I've been running a mk2.5 (not 2.5s) for many months now without any major problems, but recently I started getting more failed prints so I decided to recalibrate.

Big mistake. Although my printer was working ok before with the odd failed print, I am unable to run the calibration at all and now have an uncalibrated printer.

Running the wizard, it gets through the initial checks ok and then gets to the part where it asks you to move the carriage all the way to the top, and press the knob. I do this, and it moves itself back down, but every single time it fails when it gets to the bottom.

The interesting thing is, when it gets to the bottom the sensor is quite far from the circle on the heated bed. I believe this is why calibration is failing - it can't detect the point that it is looking for, so it gives up rather than continue down and crash into the bed. I can't work out why the printer would put the x/y in a position where it would be so far from the sensor before asking to be moved up/down, because it will never find the control point this way.

I checked the end stops and they are both hit by the print bed (y) and carriage (x) so that isn't the issue.

Any ideas how I can solve this would be much appreciated. As things are I've gone from a working printer to... well, no working printer!