LCD Error & Alarm Code Reference

Like the MK3S+, the MK4's firmware actively monitors temperatures, fans, and now the loadcell during printing, halting rather than risking damage. Treat every alarm as "stop and investigate."

THERMAL RUNAWAY / HEATER FAIL

Same meaning as on the MK3S+: the heater is on but the measured temperature isn't behaving as expected. Usually a thermistor or heater cartridge wiring fault on the Nextruder. Power off and inspect the hotend cable and its connector at the toolhead before printing again.

Selftest failure on boot

The MK4 runs a Selftest automatically on power-up. A failure here (fan, endstop, or thermistor) means something needs attention before printing at all — check the specific component the message names rather than retrying blindly.

Loadcell / first-layer calibration errors

If the calibration wizard reports it can't get a consistent touch reading:

1. Clean the nozzle tip — residue from a previous print is the most common cause.
2. Confirm the print sheet is properly seated on its locating pins, not shifted.
3. Make sure nothing (a zip tie, a stray print) is interfering with the nozzle's travel to the touch points.

FAN ERROR

The same principle as the MK3S+: a hotend fan reporting stalled or slow risks a heat-creep clog quickly. Clean or replace it rather than disabling the check.

Danger: Never bypass thermal protection to "get a print to finish." These checks exist specifically to prevent hotend fires.

After any alarm

1. Power the printer off completely.
2. Inspect the Nextruder's cabling — the toolhead cable is a common wear point given it moves with the gantry.
3. Reseat connectors, then try a short test heat-up before starting a full print.