LCD Error & Alarm Code Reference

The MK3S+'s firmware actively watches temperatures and fans during printing and will halt the print rather than risk a fire or a ruined hotend. Treat every one of these as "stop and investigate," not "just resume."

THERMAL RUNAWAY

The heater is on, but the measured temperature isn't rising (or is rising abnormally). Usually a disconnected or failed thermistor, a heater cartridge that's come loose, or a wiring fault. Power off and inspect the hotend wiring before printing again.

MAXTEMP / MINTEMP ERROR

The thermistor reading went outside a sane range — almost always a wiring or connector fault rather than an actual temperature problem, since real hotend temperatures can't jump that fast.

HEATER FAIL — TEMPERATURE DROP / NOT RISING FAST ENOUGH

Similar family to thermal runaway: the firmware expected temperature to climb at a certain rate and it didn't. Check the heater cartridge connection and make sure the hotend fan/cooling isn't overpowering the heater.

FAN ERROR / HOTEND FAN

The hotend (not the part-cooling) fan's speed sensor reports it has stopped or slowed below a safe threshold. A stalled hotend fan quickly leads to a heat-creep clog. Clean dust out of the fan or replace it — don't disable the check.

"PRINTER IS NOT RESPONDING" / EMERGENCY STOP

A safety print was halted by the Emergency Stop routine, often triggered by one of the alarms above, or occasionally by a power fluctuation. Check the alarm history in Settings → Temperature before simply restarting the print.

Danger: Never bypass or disable 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 wiring at the hotend (heater cartridge and thermistor connectors are the most common failure point on the MK3S+'s moving hotend).
3. Reseat connectors, then power back on and try a short test heat-up from Settings → Temperature → Nozzle before starting a full print.