I'm having trouble getting my MendelMax 2's heatbed not to heat up when I want to print without it. I don't get how multiple sources of control relate to each other (same with extrusion temperatures, actually):

  • Slic3r (1.2.9) has settings under Filament Settings / Filament / Bed, for First layer and Other layers (and groups of settings can be saved).

  • The pronterface GUI (Printrun-Mac-10Mar2014) has an "Options" panel where you can set "Bed temperature" (actually, two settings, one for PLA and one for ABS -- though I doubt the software can test which filament is loaded!)

  • The pronterface GUI also has a menu/fill-in labelled "Bed", which works fine to adjust the bed when nothing is printing. The menu there lets you pick from a manually-entered value, "0 (off)", and (apparently) the settings for PLA and ABS from the options panel.

  • Marlin's Configuration.h has settings for bed minimum and maximum temps (the non-zero minimum seems to be to prevent running the bed when the thermistor isn't working, to avoid unlimited overheating).

I recently tried to print some PLA with no bed heat (using blue tape on the glass build plate). I sliced the model with bed heat off in Slic3r; changed the PLA bed temps in the printerface options panel to 0; and picked the PLA setting in the GUI main screen (and also tried setting "0 (off)" manually.

When I started to print the object, the bed turned on and stayed on, maintaining 60C.

I thought of just unplugging the heatbed, but then I expect the print would never start, since it would try to heat up the bed and never succeed.

So how does the decision about which temperature setting to use, really get made? I have the same question about extruder temps, speeds, accelerations, and other things, too -- whose settings are really in charge?

  • $\begingroup$ Can you generate some g-code and put it in pastebin or somesuch? Does your bed heat up right after you turn on the power? $\endgroup$
    – abruski
    Feb 26, 2016 at 11:19
  • $\begingroup$ I should be able to grab the gcode, will try. Heatbed doesn't come on immediately, so it'd not just bypassing all control; and it maintains temp correctly at 60V... $\endgroup$
    – TextGeek
    Feb 26, 2016 at 21:18

2 Answers 2


3D printer get the temperature settings from g-code file. The firmware settings for min and max temperature are just safeguards.

You should verify instructions within the g-code file. If you are not familiar with g-code, take a look to wikipedia. List of g-code instructions for marlin firmware is here.

Instruction responsible for setting bed temperature are M190 and M140. Open your g-code file and search for lines containing them. If you delete these lines then the bed temperature will be not set during print. Additionally it means that it is set by your slicer.

In Slic3r you should check Printer settingsCustom G-codeStart G-code if it contains one of mentioned instructions and possibly remove it.


Sli3er will control the bed temperature during a print. The options in Pronterface can be used to pre-heat the bed and hot end, or to adjust the temperature during a print.

The slicer will put the temperatures you set in the filament tab settings into the gcode at the appropriate layers. As the printer reads these codes it will adjust the temperatures. If you manually change the temperature, it will stay at your adjustment until it encounters a line in the gcode file that tells it to change again. Usually this only happens at the start of a print, or at the transition from the first layer to the second layer.

When you change the filament settings in Slic3r, they do not save automatically, so if you changed them, closed the program without saving your filament settings, and opened it later, the changes would be lost.

The other place where temperature can be changed from is in the custom gcode settings, where you can specify operations to be performed at the start of the print, in between layers, or at the end of the print. Take a look there and make sure that there are no codes to change temperature in any of these fields.


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