I have a Folgertech Prusa i3, on a Ramps 1.4 with Marlin and I use Repetier-Host to control it. I am attempting to convert it to a dual extruder Bowden setup, and I can't seem to get the second extruder to work, although the first works just fine.

This is my problem:

I am not getting a reading in Repetier-Host for the thermistor of the second extruder. It is at a constant 100C. When I turn on the cartridge heater for the second extruder in Repetier-Host, the cartridge heater does not heat up.

This is what I have done:

For the second extruder, I connected the wires from the thermistor to the pins for T2 and the wires for the cartridge heater to D9. I have not updated anything in the Marlin firmware. In Repetier-Host, I selected that there are two extruders, and a second extruder is indicated under the 'manual controls' tab.

This is what I have double checked:

I confirmed the second thermistor works because it indicates a proper temperature reading when plugging it in both T0 and T1. I confirmed the second cartridge heater works because it heats up when connected to D10.

I apologize in advance if this is an amateur question, but I can't seem to find an answer anywhere. If somebody could at least point me in the right direction, or let me know if there is something I did not include in my post, I would really appreciate it, and hopefully it would help somebody else coming across a similar problem.


  • 4
    $\begingroup$ i think you would need to recompile the firmware and set #define EXTRUDERS 2 then #define TEMP_SENSOR_1 <type> etc etc. there are plenty of tutorials on the net $\endgroup$
    – fukanchik
    Commented Apr 25, 2016 at 2:55
  • 1
    $\begingroup$ It sounds like you need to modify various settings for the 2nd extruder. They are in Marlin, mainly in Configuration.h and pins.h. It's a bit of a pain since there are many #ifdef switches for different boards, printers, etc. Be sure you keep spare copies as you work. Try to work out just which #defines are getting applied in your situation, or just change all of (for example) the TEMP_SENSOR_1 #defines. It's tedious but doable. $\endgroup$
    – TextGeek
    Commented Apr 30, 2016 at 15:21
  • $\begingroup$ @TextGeek I appreciate the comment, and the direction to examine my firmware. That was indeed where my problem was. I now have it working. $\endgroup$
    – Alex Sky
    Commented Apr 30, 2016 at 20:45
  • 1
    $\begingroup$ @fukanchik I appreciate the comment, and the direction to examine my firmware. That was indeed where my problem was. I now have it working. $\endgroup$
    – Alex Sky
    Commented Apr 30, 2016 at 20:45

1 Answer 1


Thanks to the comments, I was able to narrow down the specific issues in the firmware. The firmware version was really out of date, so I recommend finding the latest stable version.

Therefore, I found the latest stable version of Marlin, downloaded it, and created my own edited version. I went line by line in configuration.h and configuration_adv.h, with the old version I had side by side to the newer version, making any and all appropriate changes. Below are the lines I found most important to evaluate when setting up a second extruder.

Make sure the you have the right board selected from boards.h:

#define MOTHERBOARD 34

Make sure the # of extruders is specified:

#define EXTRUDERS 2

Make sure the sensor is active:

#define TEMP_SENSOR_0 6
#define TEMP_SENSOR_1 6
#define TEMP_SENSOR_2 0

This should be considered:

#define HEATER_0_MAXTEMP 240
#define HEATER_1_MAXTEMP 240
#define HEATER_2_MAXTEMP 240
#define BED_MAXTEMP 90

Everything under this comment should be looked at:

// Preheat Constants

These would allocate the second extruder for other motors:


I'm sure there are other parameters I may have missed, and these are specific to my Prusa i3, but I hope this helps out anybody else in the future.


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