Single and Dual Extruder hotends, can i freely swap them?

Hi all,

I have a TAZ 4, which had the single extruder Hotend it originally shipped with, and it was working and printing fine. I later picked up the Dual Extruder hotend and went through the process of upgrading the firmware for dual extrusion. I have been happily printing ABS / HIPS with it now for a while.

However, now I want to switch back to the single hotend for a bit (which has a fan) and dedicate this original hotend for printing PLA. When I did the swap and turned it on I just get a “ERR: MINTEMP” message on the display when I power it on. I reconnected to the original “black” cables coming from the power supply.

My question to you is it possible (supported) to swap between these hotends, and if so is there a setting or something I need to flip to get it working again?

I also noticed one some other threads that some folks said it could be a disconnected or broken wire, but I don’t see anything obviously disconnected, and it was packed away with care ? Any troubleshooting tips folks have would be welcome.


It seems the temperature sensor is not being detected. You get this error when you disconnect the temp sensors. Perhaps the firmware upgrade to account for two extruders is the cause?

Yes I was also thinking that could be the cause, but I am not sure how to tell it which hotend is being used. Is there a setting I can change to tell TAZ to disable the 2nd hotend?

By default the dual extruder firmware wants to see a second extruder connected. Not sure how to change / get around that.

You can stop the error by plugging a fixed resistor into the second extruder thermistor cable connector, something about 100K ohms will give a temp reading of about 25 degrees C. Of course you could also purchase the thermistor from Lulzbot and plug it into the second extruder thermistor cable connector too. I did this when I built my Flexystruder so I could test the harness and stepper motor without heating up the hotend, a resistor of about 4.7K gives a temp reading of about 220 degrees C. The thermistor is an RTC type so the resistance decreases as the temperature increases. Here’s the RTC curve for the thermistor:


There’s two options currently for those wanting to switch between the single extruder toolhead and the dual extruder toolhead:

  • Reflash the firmware from dual > single when you switch back and forth as the firmware expects to see two extruders when enabled and will prevent you from doing things as a form of fault protection.


  • Leave the dually firmware installed. Purchase a 100k Honeywell thermistor and make a short jumper that attaches to the orange wire pair on the second extruder. The firmware will detect the thermistor on the second extruder harness and will function normally, save for only having one hot end/extruder.

We use these connectors:

Male connector pins, 24-30 AWG Digi-Key 16-02-0108
Female connector pins, 22-24 AWG Digi-Key 16-02-0102
Male Housing Connector 4POS .100 Digi-Key 0701070003
Female Housing Connector 4POS .100 W/LATCH Digi-Key 0050579404

100k Honeywell thermistor:

edit: Ninja’d! You all rock!

Thanks all, I will give the solutions a try.