Heat Bed Runs immediately after plugging in Duet.



  • I have been printing with my printer pretty regularly the last couple of weeks. When i went to go and turn it on this morning I had noticed that the head bed passed up its targeted temp and just kept going. When i unplug the Duet and re plug it back in, the heat bed now starts climbing even though I have not set any temps.

    I thought I would reach out to the forum for suggestions on the issue before i start pulling wires and troubleshooting.

    Any ideas?


  • administrators

    Disconnect the negative bed heater wire from the Duet and tape it safely out of the way, leaving the positive one connected. Then power up the printer. One of two things will happen :

    • if the bed does not get hot but the bed heater LED on the Duet lights up, either the Duet is faulty, or it is being configured to turn the heater on at startup.

    • if the bed starts heating and the bed heater LED is out, you have a short between the bed heater negative terminal and ground.



  • Thank you as always for your help.

    I unplugged the negative wire directly from the duet and had it taped up and turned it on.

    The bed appears to be now staying constant with room temperature and the LED is staying ON. I have also not changed any settings on the printer in a while. Is there one specifically i should be looking at?

    Any ideas?

    Also, this little temp run has given me a reality check that I have to be sitting here in the same room at all times while this thing is printing. This bed got extremely hot before i noticed. I am wondering how far it would have went before i caught it. How does everyone else handle this? Is a 24 hour print really involve sitting in a room for 24 hours watching it?



  • A common solution is to add a thermal fuse attached to the bed inline with the power wire. If it exceeds the rated temp of the fuse it melts and breaks the circuit. The fuse then needs to be replaced before the bed can heat again.


  • administrators

    @targenaut said in Heat Bed Runs immediately after plugging in Duet.:

    Thank you as always for your help.

    I unplugged the negative wire directly from the duet and had it taped up and turned it on.

    The bed appears to be now staying constant with room temperature and the LED is staying ON. I have also not changed any settings on the printer in a while. Is there one specifically i should be looking at?

    Try booting up the Duet with the SD card removed. If the bed heater light turns on, the Duet is faulty. If it is under warranty, please ask for it to be repaired or replaced. I am assuming there is no possibility that the bed heater terminal spill is shorting against anything underneath the Duet.

    Also, this little temp run has given me a reality check that I have to be sitting here in the same room at all times while this thing is printing. This bed got extremely hot before i noticed. I am wondering how far it would have went before i caught it. How does everyone else handle this? Is a 24 hour print really involve sitting in a room for 24 hours watching it?

    Two options:

    1. Choose the bed heater power so that even at full power continuously, the bed will not reach a dangerous temperature.
    2. Use a thermal fuse as has already been suggested.

    Similar considerations apply to the hot end.

    I never leave the house while any of my printers are operating. Sometimes I am in the next room, but I leave the door open so I should smell something if a printer overheats, I have a fire extinguisher just outside the room, and I check the print frequently.



  • Thank you again for all the details.

    I tried removing the sdcard and it appears to start up with LED light ON and some values missing from the duet's screen now. It sounds like i need to see if it under warrenty. It was purchased in 2016 so im sure if anything, i would be under something limited. I will begin that process now.

    Thank you for ideas on some suggestions to combat this. Up until now it appears like i have had a false sense of security as I know there are some temp checks within the settings but they do not appear to prevent this specific one. I will be performing one or both of the suggestions provided. I will also be removing it from my house as im sure that with issues like this I would expect difficulties \ trying to retrieve any fire insurance while it is located inside and probably an issue with coverage.

    I was in the next room for this one, It was my kid that alerted me to the smell that was coming from the room due to the excess heat. A fire extinguisher was on hand and next to the printer.

    Thank you again for all of your help. This was a scary one. Hopefully all the nervousness will settle and well get back to printing at a regularly schedule.


  • administrators

    FWIW I can only remember one other instance of a Duet bed heater getting stuck on, and we have sold many thousands of Duets. But that's small consolation if you are one of those two users.

    Which country are you in?



  • @dc42 It does help. I do not view one in thousands as reason for alarm or improvement. I thought it was a rare case as I did try to find similar situations before posting without a lot of luck. Your comment seems to verify that.

    Thanks for the assistance and im sure after some time I will get settled about the situation. It was more just me recognizing what i had of value in that room alone and being in a bit of panic about it.

    I also still havnt ruled out that it wasnt something I did as this was running perfectly before this.

    And, I am in the United States.



  • @targenaut you can find some information about implementing a thermal fuse here: https://drmrehorst.blogspot.com/2017/07/ultra-megamax-dominator-3d-printer-bed.html?m=0


  • administrators

    @targenaut said in Heat Bed Runs immediately after plugging in Duet.:

    @dc42 It does help. I do not view one in thousands as reason for alarm or improvement. I thought it was a rare case as I did try to find similar situations before posting without a lot of luck. Your comment seems to verify that.

    Thanks for the assistance and im sure after some time I will get settled about the situation. It was more just me recognizing what i had of value in that room alone and being in a bit of panic about it.

    I also still havnt ruled out that it wasnt something I did as this was running perfectly before this.

    And, I am in the United States.

    You've now been in touch with Duet3D and we've established that your Duet is a version 0.8.5, not a Duet 2. I'm not involved with the Duet 085 because that was a product of Think3Dprint3D, not Duet3D. However, as you are in the USA one option for you would be to ask forum user W3DRK if he can give you a price to mend the board. He is very competent and does Duet 2 repairs for us.


Log in to reply