Sneaky failing thermistor masquerading as a clogged nozzle

I’ve been fighting clogging for a while. Some prints work, many don’t. The same print which worked will clog on the next print. And print quality has been kind of inconsistent. Bad filament, I thought? But switching didn’t resolve the problem.

Today, after a frustrating series of attempts to fix clogging, I finally decided to try switching from an all-metal hotend to a PTFE-liner-to-the-nozzle setup to see whether heat creep was my problem. (I have both styles of heat break for this setup, I just needed to cut a new piece of PTFE tube a different length.)

As I started to test with the swapped nozzle, Klipper errored out because the nozzle exceeded 400°C. Funny, it didn’t feel like it was that hot! I worried about PTFE fumes. At least we don’t have pet birds. Then I watched the temperature report keep climbing, up past 600°C. That seemed unlikely. I waved my hand near the hot end and it didn’t feel hot. I gingerly brushed the sock. It was only warm. I removed the sock and discovered I could touch the hot end.

I wonder how long this thermistor has been going bad?

The last time I had to do maintenance on the hot end, the cartridge had fused so thoroughly to the heat block that the heat block was damaged when I finally got the cartridge out. No problem, I was interested in swapping it out for a copper heat block I had already purchased anyway. That’s when I discovered that the copper heat block (as well as another aluminum volcano heat block I had) had no support for 3mm thermistor cartridges, only bare thermistors. I happened to have one bare thermistor in my spares and installed it, grumbling.

I think my hate for the bare thermistors has been validated. I had no idea that my clogging problem was probably just the nozzle being too cold, inconsistently, probably due to damage to the delicate thermistor, even though I tried to be very careful attaching it!

Once again thankful that machining is another one of my hobbies, I drilled a #32 hole (drills tend to drill oversize, and that was closest drill size under 3mm) in the heater block. I then drilled a few mm in with a 4.2mm drill so that the thermistor cartridge wouldn’t interfere with the shoulder on the heat break. It was behind the old thermistor screw hole, and there were a few threads there, so I was able to put a small grub screw in place to hold the thermistor cartridge in place.

After four failed starts while printing the first layer, I now successfully finished a 1.5-hour print.


What printer was it?
My E3’s have the tiny bare thermisters, they look so fragile.
A few months ago mine started dying at the third layer +/- then it would make plastic Brillo…
Thus the start of my whole revamp of an Ender 3

It’s my SK-Tank kit, on which I installed an XCR3D XCR-BP6 heat sink and a 3DSWAY copper Volcano block. The bare thermistor that died was from a Cyclops kit I once planned to use and then abandoned, and the cartridge thermistor was from an XCR3D set with 24V 50W heater cartridges and thermistors.

I use an XCR3D XCR-BP6 heat sink and the BP6 heater block it comes with on my other printer. That takes the 3mm thermistor cartridge natively.

Funny you bring up this problem. I just replaced the wheels on my Y axis and replaced everything in the feed system. I too am having inconsistent prints after never having a problem. I just ordered a new hot end and we’ll see if this solves the problem. When I look at my temperature graph, it is rock steady but I think I may be running too cold also.

In healthcare we always preach never trust your monitors and always put your hands and eyes on the patient!


I did that once with a hotend and now I use a thermal gun to tell me how hot it is first.


I did have a patient try to bite me once! :tooth:


What that was cheeky! :tada:


After reading these posts I orderedCreality 3D Printer NTC Thermistor Temp Sensor 100K for Creality Ender 3/Ender 3 Pro/Ender 3 Neo/Voxelab Aquila (1m/39.4inch)
They arrived Tuesday, and as I was putting one on I found that I had crushed the previous wires by over tightening the screw when I installed my MicroSwiss hotend… Neanderthal with tools… 1 more piece of the chain replaced.