MK3S+: wrong first layer height, nozzle hits the bed or bed leveling fails (SuperPINDA)

Symptom

On the MK3S+ the first layer is too high or too squished, the nozzle scrapes or crashes into the sheet, XYZ calibration fails, or you see «Bed leveling failed. Sensor didn't trigger» or «Bed leveling failed. Sensor disconnected or cable broken».

Likely causes, from most to least likely

1. The first layer calibration (Live Z) does not match the sheet you are using: each sheet type (smooth, satin, textured) has a different thickness and needs its own profile.
2. The first layer was not recalibrated after changing the nozzle, modifying the extruder or moving the sensor.
3. The SuperPINDA sits too high relative to the nozzle: the sheet does not trigger it before the nozzle touches the bed.
4. The sensor or its cable is damaged, often by overtightened cable ties that end up breaking the cable.

Checks to tell which one it is

• Check which sheet profile is active on the printer and whether it matches the sheet fitted.
• With the extruder about 10 cm above the bed, open Support → Sensor info and put a metal object under the sensor: the PINDA value must change from 0 to 1 and the red LED on the sensor must go off.
• With the metal object underneath, move the extruder along the X axis: the value must stay at 1 without flickering.
• Compare the sensor height with the nozzle tip: according to Prusa, the sensor should sit roughly 1 mm higher.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Calibrate the first layer

   Select the profile for the sheet you have fitted and start Calibration → First Layer Calibration. Turn the knob counter-clockwise to bring the nozzle closer (more negative values) while watching the pattern, not just the number; as a guide, Prusa quotes a common range of -0.400 to -1.500.

   Check: The lines are slightly flattened, with no gaps or ridges between them.

   If that does not fix it: If the nozzle touches the sheet without the sensor reacting, adjust the SuperPINDA height (next step).

2. Lower the SuperPINDA if it is too high

   Turn the printer off and let it cool. Loosen the screw that closes the sensor holder, lower the sensor by one or two threads (or repeat the preflight check from the manual using the thin tip of the cable tie instead of its thicker centre) and tighten the holder screw again.

   Check: The sensor sits roughly 1 mm above the nozzle tip and the nozzle no longer touches the sheet during leveling.

   If that does not fix it: If the nozzle still crashes, test the sensor (next step).

3. Test the sensor and its cable

   With the extruder about 10 cm above the bed, watch the value in Support → Sensor info while you hold a metal object underneath and move the X axis. Check that no cable tie is squeezing the sensor cable.

   Check: The value changes from 0 to 1 and stays stable along the whole travel.

   If that does not fix it: If it flickers or does not change, the sensor or the cable is damaged: replace the SuperPINDA following Prusa's guide or contact their support.

4. Repeat the XYZ calibration

   After moving or replacing the sensor, start Calibration → XYZ cal. and follow the screen; the first part is done without the steel sheet. When asked, place a sheet of paper between the nozzle and the bed: it is only an indicator, not protection. If the nozzle catches the paper, press Reset immediately, lower the sensor by two or three threads and try again.

   Check: The XYZ calibration finishes without errors.

   If that does not fix it: Prusa recommends running the Calibration Wizard again from the beginning and then the first layer calibration.

Prevention

• Use a sheet profile for each sheet and choose the right one before printing.
• Repeat the first layer calibration whenever you change the nozzle, work on the extruder, move the sensor or relocate the printer.
• Do not overtighten the cable ties on the sensor cable.

Still not fixed?

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Printers it applies to

The Prusa MK3 family: MK3S+.

Official sources

This guide summarises the official documentation linked here:

• First Layer Calibration (i3) · Prusa Research
• P.I.N.D.A./SuperPINDA Sensor testing · Prusa Research
• XYZ Calibration (MK3/MK3S/MK3S+) · Prusa Research
• Nozzle crashed into the heatbed · Prusa Research