Thermal runaway error after front print fan kicks in.

After a succesful upgrade to MK2.5 all calibrations and tests succeeded without errors, selftest is fine.

After starting a print everything looks ok, but after the first layer when the front print fan starts the extruder temperature drops rapidly and leads to a Thermal runaway error shortly after.

Looks to me the airflow from the front print fan is to much directed to the hotend rather the printed part or firmware is not keeping up sensing the extruder thermistor and react accordingly.

Anyone had this issue already and found a solution?

thx Gerhard

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Hi Gerhard,

can you please post few photos here? We have many MK2.5s in our offices working, so it might be some issue with the assembly or some broken piece of electronics.

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Hi Jakub, from what specific perspective do you want photos?

I did some more investigation and it turns out that if the part fan is running at 100% it's cooling down the hotend to much. When running at maximum 80% the hotend temperatur only drops about 10° C which doesn't trigger the thermal runaway error.

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Hi Gerhard, photos of the assembled printer, namely the Extruder. Then pictures of the failed print. I will discuss this with my colleagues.

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Hi Jakub, attached the photos. The print stopped on the second layer so I didn't take a picture of it.

kind regards

Gerhard

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Hi Gerhard, sorry for a late reply. Everything on your printer from the point of the assembly seems ok to me. It might be the thermistor is reading bad values. Contact our support at info@prusa3d.com to discuss getting a replacement part.

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Have you tried a silcone sock for the hotend?

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Gerhard Wildzeisz will be eternally grateful.
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