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!
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.
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.
Also, the thermistor is snuggly attached to the printer.
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.