Thermal runaway question

Mostly Printed 3D Printer - MP3DP Advice
1

I’ve been having some trouble with thermal runaway lately on my MP3DP. It’s using a generic MK8 extruder and whatever heater and thermistor that came with it. It used to run fine before I swapped in a bunch of new parts. RAMPS with DRV8825s to SKR 1.4 Turbo with TMC2209s, 39 oz/in steppers to 84 oz/in steppers. But no changes on the heat side of things. I’ve run the auto PID multiple times and saved and verified. But say I print something, then remove the new part, a little time goes by while I load up another model or whatever and the hotend is slowly dropping in temp. When I go to run the next print job the hotend will start heating, but it seems to take a little longer than the thermal runaway threshold likes and I get halt error.

I guess my questions are… Is my heater failing? Should I run the auto PID a couple more times? Is there a way to adjust the thermal runaway threshold without a firmware recompile? TIA

2

I picked up a used Prusa MK2.5S (12V) and it had some issues with thermal runaway. First, it would take too long to heat, and would kick out a runaway error. A silicon sock fixed that. But it still had issues and I did find a flaky wire in the heater and temp sensor that was causing intermittent problems. Took some troubleshooting with a multimeter to find it. Disconnect them, hook them up a meter to measure the resistance, then wiggle all the wires and see if it drops out. Take your time and work your way down the wire a little bit at a time. Both breaks were right outside the extruder head where all the cables get the most flex.

3

Thanks for the tip! I do have a silicone sock on the heat block. I’ll check the heater and sensor out when I get a chance.