Thermal Runaway Issue (Extruder)

A few months ago, my entire heater block was caked and I had to replace everything. Thermistor, heater cartridge, heater block. I'm 100% sure these new pieces all have the right specifications to match this printer. The only exception is the heater block, which is a brass one from Mellow store, but it still fits and everything. I even got a sock to keep it from being caked again.

Only problem is, now I can't print anything anymore, because 5 minutes in, it just stops and gives me a thermal runaway issue. I tried printing with Cura, but all it did was heat up the thermistor until I saw smoke and noticed the PTFE smell. it even left a white mark on my bed and warped my scorpion duct. I guess Cura somehow bypassed the thermal runaway detection. I had PID tuned multiple times, but the values were weird so I replaced the thermistor again and it worked long enough to print a calibration cube. when I tried printing the fan duct, it happened again.

So I saw a post on here that said it could be a problem with the wire that leads to the motherboard. I tested the resistance on the thermistor, the wire, and even checked to see if the readings were fine with pronterface, it detected my finger temperature just fine, even when I shook the wire pretty good. everything seems normal.

I don't know what's going on, there's either something with the board, or the fan is too powerful? I did print the cube without cooling, but I never go above 50% because since I replaced it with a radial, my printer stops halfway through a print if it's higher than 50-75% with seemingly no errors...
or maybe the brass heater block messes up with the readings?
the hole for the thermistor IS bigger and the screw doesn't fit in properly so I'm thinking maybe I'm supposed to use muffler paste?
What should I do?


  • Laser8302Laser8302 Posts: 151Member, 🌟 Super Member 🌟
    The thermistor should make hard contact with the heater block otherwise you will overheat the block/tube. I would get a aluminum heater block that has the proper mounts for the thermistor. Something like THIS.

    I would not glue in the thermistor. maybe use some aluminum foil stuffed into the hole with the thermistor to keep it in good contact?
  • Jari ChristophersonJari Christopherson Posts: 11Active Member
    Wow, that simple aluminium foil trick seemed to have fixed it. Whew, thanks!
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