Error messages

Search this page for the text you are looking at. Klipper’s wording varies slightly between versions, so match on the distinctive part — too far in past, Unauthorized, not heating — rather than the whole line.

The printer stopped mid-print

Message	What it means	Where to go
`Lost communication with MCU 'extruder_board'`	The host stopped hearing from one of the two control boards. Usually a USB or power problem, not the board	Klipper MCU communication lost
`mcu 'mcu' shutdown: stepper too far in past`	G-code with thousands of micro-segments — curves exported from CAD rather than sliced. The board cannot consume the moves fast enough	Layer shift
`MCU shutdown` / `Lost connection to MCU`, at idle or overnight	Same family. If it happens with the machine sitting still, suspect power or the SD card	Klipper MCU communication lost
`Lost communication with MCU 'mcu'`, the moment someone touched the machine	The emergency stop cuts power to the Octopus, and this is what Klipper says when it does. Check the mushroom before the cables	Emergency stop button
Shutdown that coincides with the vacuum starting	The pump’s inrush drops the supply. Split the load across the two mains inputs	Hopper suction problems

Heating and temperature

Message	What it means	Where to go
`Heater extruder not heating at expected rate`	The zone is not gaining heat as fast as Klipper expects. A physical fault — sensor wiring, relay, or the band — never a tuning problem	Heater not reaching temperature
`extruder below minimum temp`	The zone reads below the floor. Almost always an open circuit — a deeply negative, flickering reading around −90 °C, not a cold barrel	Temperature sensor disconnected
`temperature not valid`	Same cause. The firmware minimum is 0 °C, so a negative reading is rejected outright	Temperature sensor disconnected
A zone reading about −90 °C	Not a temperature. The board sees infinite resistance, which the sensor curve maps to the bottom of its scale — the signature of a break in the wiring	Temperature sensor disconnected
Temperature drops when the fan runs, then a heating error	The part-cooling fan is blowing on the sensor, on machines where it sits outside the barrel insulation	Temperature sensor disconnected
The bed reports over 110 °C and the printer shuts down	The bed’s firmware limit. If the bed is still hot afterwards, it is on the wrong socket	Bed heater on wrong outlet
Extrusion refused with the barrel apparently warm	Klipper will not extrude below 160 °C (`min_extrude_temp`). Check which zone is short	Specifications

The interface

Message	What it means	Where to go
The printer’s own display shows `Unauthorized`, browser works fine	Moonraker was updated to 0.11, which the display’s software cannot authenticate against	Display stuck after a Moonraker update
`Error getting Moonraker server info: Unauthorized`	The same fault, in full	Display stuck after a Moonraker update
`Klippy is not running` banner in the browser	The Klipper host process stopped. The reason is printed in the Console	Mainsail dashboard basics
`Klippy not connected`, or the page says Disconnected	Same. A Firmware Restart usually brings it back — and if it does not, the Console says why	Firmware restart
`g1os.local` does not resolve at all	Name lookup, not the printer. Use the IP from your router	Mainsail dashboard basics

Bed levelling and the probe

Message	What it means	Where to go
`probe triggered before movement`	The switch is already closed before probing starts — a stuck plunger, or plastic under the nozzle holding it	Probe arm bending
The head drives into the bed with no trigger	The switch never fired. Check it clicks by hand before suspecting anything else	Probe arm bending
`LOAD_MESH` finds nothing to load	No `global` mesh has been saved yet. Run `BED_LEVEL` once	Bed leveling system

When the message is not the fault

Two of these mislead often enough to be worth stating plainly.

A temperature error is usually a wiring error. extruder below minimum temp, temperature not valid and a −90 °C reading are all the same thing: a break somewhere between the board and the sensor. Replacing the sensor moves the fault to a new part.

stepper too far in past is not a mechanical fault. Nothing is loose. The G-code is asking for more moves per second than the board can execute, which is what happens with curves exported straight from CAD.

Print quality — which page — when there is no message, just a bad print
Mainsail dashboard basics — the Console is where Klipper says why
SSH access — reading klippy.log when the interface will not show it