I am trying to port Marlin to my Qidi Tech 1 printer which previously ran Sailfish 7.8. Everything worked fine on the old board, including the temperature sensors.

All cables except for power, LCD, and USB (for flashing) are disconnected. I am still very early on in testing and have yet to plug anything else in.

When uploading Marlin to the board, at first startup I received the following error:


Please Reset

There may be a problem with my configuration. So I commented out all of the thermal runaway protection options since the bed and extruders aren't yet connected:


I rebuilt, flashed, reset, and the printer is still telling me that E1 is at MAXTEMP.

Why am I still getting this thermal protection message?

I cleared the EEPROM from the LCD menu in Sailfish before flashing.

This board uses an ATmega2560 and I'm using the default fuses (E:FD, H:D8, L:FF, LOCK:CF).


2 Answers 2


#define THERMAL_PROTECTION_HOTENDS is for thermal runaway. When the temperature "should" be climbing or falling at a predicable rate, or holding steady once at running temp.

#define HEATER_0_MAXTEMP defines the maximum temperature Marlin will allow the extruder to get to before initiating a shutdown. This is ALWAYS active for an active extruder (E0) This setting is what will throw MAXTEMP if it is exceeded.

MAXTEMP error when there is no heat on is usually from a short in the thermistor cable.


MAXTEMP and MINTEMP are not part of the Thermal Runaway Protection, but separate, equally needed safety nets: Mintemp is meant to make sure that the printer does not try to run cold, Maxtemp is the operational limit of your printer - if the machine tries to go hotter, the firmware denies and shuts down. Maxtemp is usually set to about 235 °C for a lined hotend.

A defective thermosensor can trigger Mintemp and Maxtemp errors by virtue of either shorting or by having no connectivity. The same behavior is exploited in a simple test if the triggers are set: disconnect the leads for unlimited resistance that the board interprets as an absurd high temperature, then short the leads, as 0 Ohm registers as an insanely low temperature.

  • $\begingroup$ If this error keeps showing up at operating temps (e.g. 210C) would that imply that the thermistor is bad? (I'm having a similar problem with one of my printers right now). $\endgroup$
    – user77232
    Dec 12, 2020 at 22:02
  • $\begingroup$ @user77232 it can point that out, yes. Mintemp and Maxtemp can be triggered manually by disconnecting and shorting the leads of a thermosensor $\endgroup$
    – Trish
    Dec 13, 2020 at 0:47
  • $\begingroup$ When I restart my printer it reads 300c. What does shorting the thermistor leads actually cause the temp to read? Would it just read MAX? $\endgroup$
    – user77232
    Dec 13, 2020 at 13:31
  • $\begingroup$ @user77232 300°C sounds abotu what a short or near short will read. It should trigger maxtemp a few seconds later. $\endgroup$
    – Trish
    Dec 13, 2020 at 14:42

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