I'm having an issue with my Prusa i3 MK2 MMU.

It starts printing just fine, and everything gets up to operating temp quite quickly. However, after printing the first few layers, it seems as if the heated bed can't keep up with the demand, and its temperature starts to drop, first it can barely hold 80 °C and then it slowly drops down to 77-76 °C before the printer shuts off due to BED THERMAL RUNAWAY.

The LED is continuously on for the bed, so it seems to be supplying power when this happens. Setting the printer down from high power to "silent" helps a bit, so could this be that it is not getting enough power?

Ambient temp is around 17 °C.


1 Answer 1


The local library makerspace (prior to COVID-19 shutdown) has a Prusa i3 MK2 (no MMU) that had a similar problem. The model being printed was relatively small, compared to the bed and was being printed nearly atop the temperature sensor.

The part cooling fan was cooling the bed sensor while the rest of the bed was not being used.

Moving the model away from the sensor resolved the problem. If you're printing in the center of the bed, consider to re-slice in a position offset from the center.

If you are using the PEI sheet as the library machine is/was, consider to shuttle your prints around the bed over time. The library's printer wore away the PEI from always-centered prints. It had to be replaced after about a year. The replacement is going on two years with little complications.

  • $\begingroup$ Spot on mate, I was printing a ½ inch cylinder in the middle of the bed. I'll try moving it around and see if that helps! Thanks! $\endgroup$
    – Stuggi
    Mar 28, 2020 at 22:59

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