Labists ET4 printer nozzle hits bed after automatic levelling I use Slic3r to create G-codes for my Labists ET4 printer. Usually, no problem.
Now, as soon as I tried to start a print, the nozzle head went down as usual, but this time it went a bit lower than 0 and the machine made angry noises for less than a second.
It went back up again and heated the bed and the nozzle, only to go back down too strongly with angry noises again. Even left a little pokey hole on the bed.
I got scared and turned the machine's switch off and manually raised the Z axis with ease.
Never had this problem before and now I'm afraid to turn on my machine.
I've had the following setup for G-codes prior to today's incident and it had worked just fine:
G28 ; Home extruder
G1 Z15 F[travel_speed]
M106 S[max_fan_speed]; Turn on fan
G90 ; Absolute positioning
M82 ; Extruder in absolute mode
; Activate all used extruder
M104 T0 S[first_layer_temperature]
M190 S[bed_temperature]
G92 E0 ; Reset extruder position
; Wait for all used extruders to reach temperature
M109 T0 S[first_layer_temperature]

After this, I did try the auto levelling, however it still tried to plow into the bed, albeit not as angrily.
Here's other things to potentially consider:

I haven't used the machine 10 days.
It's been chilly in the room where the machine is.

So here's my questions:

&quot;What could cause a 3D printer to have an incorrect impression of Z-axis=0 even in absolute position mode?&quot;
&quot;What can I do to fix it?&quot;
Dirt. It was dirt. Most likely.

Apparently the machine establishes bed level with a sensor, and I might be wrong, but I think the ET4 monitors capacitance as a means to notice how far the nozzle is from the bed.
After all else failed I looked at the nozzle closely and noticed that the whole thing looked fuzzy. Looks like soot (from where though!?) had settled on the machine's sensitive components and de facto blind-folded its sensor.
A wipe and a levelling later, all was back to normal. Yay!