I'm printing basically a large flat square pane. This goes fine for 3 layers, after which the temperature suddenly drops by about ten degrees. After a while, my printer goes into thermal runaway protection.

I restarted my print, and as soon as the temperature drops, I pause the print. I wait for it to go up again, and resume. It starts dropping again, so I decide to see about continuing this part at 200 degrees (which worked quite fine, so I think I'll stick at 200 for now.)

Temperature suddenly drops to 200

I have tested running the printer at 210 and turning on the fan, thinking maybe it's simply related to that. That does not give a thermal runaway, and a drop of 2 degrees max. My assumption is that it's the PID.

How do I fix this?

My printer is a heavily modified Anet a8, running Marlin.

  • $\begingroup$ Can you measure the hot-end temperature independent of the sensor to tell if you are really getting the temperature drop then thermal runaway, or is this a problem with the sensor? $\endgroup$
    – Perry Webb
    Commented Oct 29, 2020 at 14:12
  • $\begingroup$ I can not, don't have tools for that. But considering that it rises again as soon as I pause, I'm assuming I am really getting a temperature drop. I highly doubt there is any actual thermal runaway, considering that the temperature does remain stable at 200. So, without any tools to definitively confirm, that rules out an actual runaway for me. $\endgroup$ Commented Oct 29, 2020 at 14:15
  • $\begingroup$ Did you test the 210 °C with full part cooling test near the bed or in the air/at certain Z height. $\endgroup$
    – 0scar
    Commented Oct 29, 2020 at 14:17
  • $\begingroup$ I did, by pausing the print. This keeps the fan on, and the print head at the same height. $\endgroup$ Commented Oct 29, 2020 at 14:46
  • $\begingroup$ Are you sure the slicer didn't insert temperature reduction commands? $\endgroup$ Commented Oct 29, 2020 at 14:58

1 Answer 1


I had a similar problem with an Anet A8 once. The problem was, that the thermistor wasn't mounted right in the heat block, so the air flow cooled it while the print head was moving. You can check, whether this is a problem at your printer.

  • $\begingroup$ According to the OP's Octoprint screenshot, it was the target temp that dropped, not just the achieved temp, so I don't think this is a plausible explanation. $\endgroup$ Commented Oct 29, 2020 at 14:57
  • $\begingroup$ @R..GitHubSTOPHELPINGICE As I mentioned, after a while I manually lowered the target temp. $\endgroup$ Commented Oct 29, 2020 at 20:31
  • $\begingroup$ I will definitely check my thermistor. $\endgroup$ Commented Oct 29, 2020 at 20:32

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