Before I start, I'll give you my setup:

  • Ender 3 Pro
  • Marlin
  • Material/Nozzle: PETG 0.4 mm @ 215 °C
  • Bed: Glass @ 80 °C
  • Default printing speed: 70 mm/s
  • Standard part cooling fan

Since I've updated the Marlin FW on from factory default to, my printer stops printing and gives out an thermal runaway exception message.

The problem is absolutely repeatable and happens always on beginning of layer 2 (more precisely: 40 seconds after beginning layer 2). Changing PID values doesn't change anything to the moment of the error occurring.

I managed to run it longer by repeatedly dropping the temperature set-point and making a photo of the temperature plot. First photo is right after the initial drop from 215 to 205 °C. Second is when the temperature started rising slowly again.

Right after the initial drop from 215 to 205 °C

Temperature starting to rise slowly

After this temperature drop, the hotend temperature seemed to be much less stable and reached only 205 °C.

At Layer 12, the same thing happened again. But dropping the temperature far too low for PETG and having the "same" issue again, making me stop the print.

This problem is pretty urgent and I haven't found any suitable solution by now. Do you have any ideas of what may cause this trouble? New heaters and thermistors are on their way right now. But I fear that this is not a hardware problem since none of the components are damaged and dysfunctional, nor the moment of failure is random.

  • 1
    $\begingroup$ I even find 215 °C very low for PETG, care to share the brand? I'd rather go to at least 230 °C How much part cooling are you using? PETG requires very little, to none unless you print very delicate thin objects, e.g. like point of a rocket. What is the reason for updating the firmware? You could go back by flashing the original firmware. PETG doesn't like high printing speeds, lower to 30-50 mm/s frist. $\endgroup$
    – 0scar
    Dec 17, 2020 at 13:10
  • $\begingroup$ I fear I can't do that... That's pretty bad no-name stuff, having heavy bubbling issues above 230°C (even after drying with silica gel in an oven for hours). Between 205 and 220 happened to be the sweet spot with almost no stringing or bubbles and good strength. The problem is not related to the printing temperature or speed, since the error I'm trying to solve occurs completely out of a sudden. But I'll try again at 235°C and hope for the best $\endgroup$
    – jwagn
    Dec 17, 2020 at 13:30
  • $\begingroup$ I started again, printing at 235°C. Before the print failed again, I recognized that the hotend never reached the setpoint. At first sight, I'd would guess that the P-Value of the Controller may be set wrong. But looking at the heater signal (led on the mainboard) tells me that it is on full blast. Maybe a damaged heater lacking power wasn't a bad Idea at all. If changing the heater is a solution for my problem, I'll let you know. $\endgroup$
    – jwagn
    Dec 17, 2020 at 14:35
  • $\begingroup$ After the Firmware reflash, did you PID-Tune? $\endgroup$
    – Trish
    Dec 17, 2020 at 16:34
  • $\begingroup$ i did multiple times $\endgroup$
    – jwagn
    Dec 17, 2020 at 16:35

2 Answers 2


It turned out, it was a faulty heater, that wasn't able to reach and maintain temperatures over 195 °C in a stable manner. The order came, had a new 50 W heater, thermistor and a PTFE-Bowden tube. It works just fine again, now!

  • $\begingroup$ Nice to post your own solution! Please accept the answer after 48 hours. Thanks! $\endgroup$
    – 0scar
    Dec 20, 2020 at 19:43
  • $\begingroup$ Please mark your answer as the accepted answer, using the tick icon, in order to remove it from the unanswered question queue $\endgroup$
    – Greenonline
    Apr 25, 2021 at 12:14

I find my Ender 3 Max has "phases" where each and every print will end in a thermal error, always at layer 2. During these phases, I disable retraction to keep the flow of filament constant through the hot end and into the nozzle. While my prints are a little messier than I would like, more often than not they actually finish.

Another thing that helps is to lower the initial bed temperature as much as possible, or even have it at room temperature (Max has a carborundum glass bed with blue tape over the top) and raise it as the hotend moves away from the bed. I feel that layer 2 is the "transition layer" where the hotend is no longer using the heat from the bed to maintain its temperature, so the controller lets it have a big burst of energy to compensate for any temperature variations and more often than not gives it too much, resulting in our beloved E1 error.

I may be wrong, but I would love to try a thermal camera to see if it's true!

  • $\begingroup$ could this be filament dependant? that you have a different brand? $\endgroup$
    – Trish
    May 14, 2021 at 17:03

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