Lulzbot Mini Print bed temperature fluctuation

Normally my print bed stays at a pretty constant temperature within a few degrees of the set temperature for a print.

Lately it has started deviating quite dramatically from the set temp:

Any idea why it would have started doing that?


Another screen grab taken about 20 minutes later…

Hi Daniel,

Hmm, that definitely looks a bit strange. @Aidan would be the one to ask about that, when he’s in he’ll be able to get back to you.

Hi @Daniel25998,

Shoot an email to and link them to this forum post. They’ll be able to help you out pretty quick.

Thanks Graham, I’ve sent an email to them. I’ll let you know what they come back with.


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Lulzbot support have asked me to measure the resistance of the Heater Coils and the Thermistor.

So at approximately 12 degrees celcius:

Heater Coils - 5.1 - 5.2 Ohms

Thermistor - 178.9 KOhms

Since then support have asked that I check the wiring continuity between the Rambo and the print bed. After an initial false positive I’m now reasonably certain the wiring is ok.

I’m now waiting for a follow up response from the support team. I’ll post any more information here when I learn anything.

30-JUN: Support have asked me to test the printer using Cura to see if the temp fluctuations occur. I’ve only used Octoprint to drive the printer since the initial print so it will take some time to setup and run that test,


Thanks for documenting your troubleshooting progress here, Daniel - hopefully it helps anybody else who might encounter this behaviour to get in front of it even quicker.

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Here’s a photo of how I measured the continuity of the thermistor wires:

I went back and did it again using thicker hookup wire the second time to eliminate any slop in the connection. Once I’d done that the resistance readings were steady when moving the print bed around and jiggling the wiring loom.

Support suggested that I try to print using Cura itself rather than Octoprint.

So, I’ve done 3 prints with a laptop directly connected to the printer and did not observe the same issue. I’m going to do exactly the same thing with the Octoprint on the Raspberry Pi to see if the problem returns.

As a side note: I think my PEI sheet might be on its last legs…

Also: Do you sell replacement hot-end fans? Mine seems to have developed a rattle… I can’t see one on the online shop. And I should point out that the “Printer Chassis” category pages currently shows no products in it…

So, 3 further prints, this time using the Raspberry Pi and Octoprint and the fluctuation behaviour has not exhibited again…

I’m really confused now…


Hi Dan,

The heatbed patterns you shared earlier suggested (to me) an intermittent connector somewhere. If that was the case then disconnecting to take measurements and reconnecting may have been the fix.

You’ve done some thorough testing - so you are all set now for longer prints.

Hi Graham,

I have to agree with you… I can’t think what else it might be.

If it does come back I’ll try the disconnect/reconnect thing and see how it goes.


PS: Longest print I’ve run so far (before this problem cropped up) is about 28 hours…