Prusa MK4: Most Common Problems & Fixes

Load-cell Z calibration drift

The single most commonly reported MK4/MK4S issue. The load cell sets the Z reference for the nozzle, and that calibration drifts gradually — typically over weeks to months. Watch for first layers that used to look perfect starting to show gaps (Z too high) or scrape marks (Z too low), and recalibrate when you notice either.

First-layer vibration

Tolerance variance between the toolhead carriage, bearing mounts, and planetary gear can produce noticeable vibration, especially on the first layer. Check the toolhead assembly for any looseness and confirm you're on current firmware, since Prusa has iterated on this.

Hotend not reaching its advertised temperature

A commonly reported gap between spec and reality — many units top out closer to 290°C rather than the advertised 300°C. Avoid planning prints that depend on hitting the very top of the advertised range.

PSU strain during simultaneous heating

The stock 240W power supply can be pushed past its limit when the bed and hotend heat simultaneously, dropping voltage and potentially causing a driver brownout. Avoid running other high-draw accessories during initial heat-up, and keep firmware current for its heating-sequence tuning.

ABS warping from an overly aggressive part-cooling fan

The stock 5015 fan is powerful enough that even 10% power can unevenly cool large ABS parts. Reduce the cooling fan percentage further for ABS/ASA, or disable it entirely for the first several layers.