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I have an Anycubic i3 Mega-S and when I'm printing something (especially when it's hotter) the temperature increases and decreases by around 3 degrees during the print. Is this normal?

I was worried this is a loose thermistor and if it comes out during a print my house will probably catch fire! I have no idea how to tighten it though.

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  • $\begingroup$ Welcome to 3dPrinting.SE! While I'm no expert, I've seen the same fluctuations while using my Anet A8 clone printer. I've not seen any detrimental effects due to it. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Mar 25 '19 at 13:54
  • $\begingroup$ :O after reading this question I went to print, then the temperature started to fluctuate from 175° to 215°, then temp error, so I found the sensor connector was loose, temp error was fixed, then fluctuation temp was only on preheat only, but suddenly the PSU burned out!!! The PSU was shorted circuit. $\endgroup$ – Fernando Baltazar Apr 16 '19 at 18:59
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All printers will have some fluctuation and it's not a concern. This is similar to the fluctuation you'll see in your home temperature around the thermostat setting. There are a couple reasons. One is that the feedback loop (thermistor to control board to heater to extruder block) will always have some lag. Another is that most systems have built-in "hysteresis," i.e. set the "turn off heat" a couple degrees above the "turn on heat" thresholds. This avoids "chatter" from on to off right at the setpoint.
Some thermistors (e.g. my AnetA8 clone) can be held in place with a setscrew. If yours doesn't have a similar capability, use Kapton tape to hold it in. This tape is designed for high temperature operations so it won't age or collapse, and it has good holding strength.

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