<p>A few weeks ago I got a thermal runaway message on my modded Ender 3 during a print, and I have not been able to get it working since then! I have tried fixing and replacing everything, and I still keep getting the message!</p>
<p>When the printer starts/heats up, the thermistor is able to read the temperature with no problem, but when a print starts, the thermistor starts reading strangely and I get the thermal runaway message! Basically, whenever I start a print the temperature being read slowly drops until it gets to around 20 degrees below the set temperature. I then get the thermal runaway message.</p>
<p>So far, in an attempt to fix it, I have replaced the thermistor twice, the heating element, the wiring was replaced, the firmware and even the entire motherboard! I have no idea how/why I’m still having the message, it just doesn’t make sense.</p>
<p>Also, the thermistor is snuggly attached to the printer.</p>
<p>Please note I’ve tried another thermistor that was glass and had the exact same issues. This lead me to think that this had something to do with the heating element being overwhelmed by something. So, as a test I simply just extruded filament from my nozzle with my fan on to see if that would have the same effect and it didn’t! The temperature stayed up fine. This is leading me to believe that this is some sort of issue with starting a print. Maybe a G-code issue.</p>

[{'answer_id': 17871, 'author': 'Kezat', 'author_id': 30645, 'author_profile': 'https://3dprinting.stackexchange.com/users/30645', 'pm_score': 1, 'selected': False, 'text': '<p>If the error only happens when the printer starts moving it\'s logical that the issue is in the wire loom that starts to bend and flex once the print starts.</p>\n<p>As a quick test and if your comfortable with a little wiring work a temporarily line could be connected directly from the sensor to board. Skipping rewiring the loom until its confirmed to be the issue.</p>\n<p>Same logic for the heater wires if it has a connector at the extruder.</p>\n<p>Another potential cause for this is if the extruder is already near printing temperature and a new print is started, the printer could think that the temperature shot up way faster then expected even though in reality it was just a bit preheated. If you made any changes to your start G-code, like changing the heating command type or order in witch the extruder/bed is heated, see this stack: <a href="https://3dprinting.stackexchange.com/questions/13353/thermal-runaway-triggers-when-raising-temperature-amid-cooldown?rq=1">Thermal runaway triggers when raising temperature amid cooldown</a>.</p>\n<p>Edit:\n<a href="https://www.youtube.com/watch?v=JcG7fIcF24k&amp;ab_channel=DaHaiZhu" rel="nofollow noreferrer">This video</a> demonstrates a test to show if Thermal Runaway is enabled. While this setting is not in question here it might be a way to troubleshoot the underling cause for this kind of issue. If the extruder temperatures drop rapidly the same way it does when a print is attempted it might show that the temperature sensor is reading the correct temperature. And thus may indicate a issue with the extruder heating system and not the temperature sensor itself.</p>\n'}, {'answer_id': 17879, 'author': 'fred_dot_u', 'author_id': 854, 'author_profile': 'https://3dprinting.stackexchange.com/users/854', 'pm_score': 0, 'selected': False, 'text': "<p>I've had this problem on a Prusa MK2s. The print was always at the center of the build plate and that's the location (underneath) of the thermistor. The part was small, the cooling fan was chilling the bed at the same time it was trying to maintain temperature. Moving the part a few centimeters away from the center resolved the problem.</p>\n<p>In the case of this PEI coated bed, always centering the print caused the PEI to wear in that area, requiring replacement. The operators were informed to place the build in random, non-centered locations in the future.</p>\n"}, {'answer_id': 20066, 'author': 'Michael Lamont', 'author_id': 35676, 'author_profile': 'https://3dprinting.stackexchange.com/users/35676', 'pm_score': 0, 'selected': False, 'text': "<p>Soo I cleaned my hot end completely took it all apart cleaned it inside and out put it back together and I fix my thermal runaway e1 now my printer runs fine I'd say start there</p>\n"}]
['https://3dprinting.stackexchange.com/questions/17870', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/30669/']