Hotend too cold - doesn't match thermister reading

I have reasons to believe that the hotend of my Mini v1 gets too cold to extrude filament, even though Cura is showing that the temperature is correct. I’ve found it printing in mid-air because the gear has ground through the filament. And during a filament change I couldn’t push the new filament (PLA) through the nozzle, even though the temperature was shown to be 210.

When this occurs the hotend is hot, but it doesn’t seem to be as hot as it should be. I’ve ordered a tool so I can try and accurately measure it. So far this problem has been very intermittent and powering down the printer and waiting for a while seems to fix it.

I don’t know if it’s related, but another very intermittent problem started at about the same time. After leveling occurs and just before printing starts, the Y-axis, or something, bangs against the stops for a few seconds and then the printer stops, even though Cura seems to think it’s printing normally. Turning the power off and waiting for a while seems to fix it.

Has anyone seen this before and know what the problem is?

Sounds like heat creep to me. Does the print do alot of retractions? The heat can “travel” up the filament until it gets very soft near the gears and they simply mush through the plastic rather than pull it down. Turning off the power allows everything to cool off which might also explain the heat issue.

I don’t think so.

I went to manually push new filament through the nozzle while Cura said it was 210 C and it wouldn’t move. Nozzle was hot but I don’t think it was hot enough to melt the filament. I turned off the power off and tried again 20 minutes later and I pushed the filament through without any problem, as a usual. No drive gear was used, so it’s not heat creep.

So here’s my theory: the nozzle heater is working fine, but sometimes it’s not hot enough to melt the filament even though Cura says the temperature is correct.

It seems to me that if the thermistor was failing, it would be reading the temperature incorrectly almost all the time, instead of only once out out every 5 or 6 times I try to print something. Also, the problem seems to occur early during a print, within the first 10 or 20 layers of a print.

I take it back. You might be right about it being heat creep. There was some dust/dog hair? between the fan and hot end. I haven’t had any problems since removing it.

But, the problem has been intermittent and I definitely had a problem once with pushing in new filament because the nozzle was too cold, even though Cura said it was at the correct temperature. .

If you can’t push PLA filament through at 210 then it shouldn’t be heat creep. Not sure what the issue is but you should be able to manually push it through.

So you have a laser/infrared /FLIR to check what the nozzle temp reads versus the printer thinks it is?

It isn’t unheard of for a thermosistor to fail

I do have an infrared thermometer and a thermocouple that I could measure the temperature with. But I haven’t had any problems since finding and removing some dust and debris between the fan and hot end fins.

I think iguanaman was right about it being heat creep. The problem I had with pushing new filament through the nozzle might have been a fluke or user error.

I may get rid of the printer if the problem comes back. I think Lulzbot replacement parts are far too expensive and I’m impressed by the capabilities and reputation of the Qidi printers.

It wouldn’t hurt to check and verify, but if the previous troubleshooting fixed it, all is well!

On my machines, all filament goes into the filament dryer for whatever is suggested by the manufacturer. Then, I put it in a filament dry box and the printer pulls the material along from that. Moisture in the filament is extremely common and affects print quality. I’ve had better quality and less failures doing that. (I also use enclosures which keeps crap out too!) Since i just picked up this Taz used, I plan to order one for it.

I agree on the parts cost