Extruder Temperature jumping fast up/down

[frankjoke]

Dear all!

I had a large print failing because it seems that there were parts where extruder did not extrude very well.

Now I started to investigate and found that my extruder temperature, which in the past was always +-1° of target is fluctuating a lot.

Temperature

What can be the reason for that?

Another one, just started a new print :(

[andrewsi]

The thermistor in the hot end is going bad or has an intermittent electrical connection. Replace it with a new one. This seems to be a fairly common problem. There is a theory mentioned in other posts that perhaps the thermistor-in-steel-tube design isn't permitting enough room for expansion or flex and leading to cracking internally, but that's just a guess.

There are some other posts on this topic if you search the board.

[frankjoke]

Ok, I took the pain and exchanged the hotend.

I had to do something because on Extruder 0 my stepper motor cable was broken, unluckily it was too short just tto solder or repair even inside motor. Now extruder did not print reliable anymore because of the temperature problem, so I exchanged both 2day and now everything is working again (and I have a dual extruder again )

[andrewsi]

Just FYI, you shouldn't have to replace the whole hot-end: The thermistor is held in with a set screw and can be changed independently of the rest of the unit (including the heater cartridge, which is also held in with a set screw.)

[frankjoke]

When I ordered some spares they had only full built extruder, and I did not get my service parts (with drill and replacement thermristor) so far, so I replaced the full part. Anyhow thanks, know it for next time!

Actually I was happy that I had a motor, a fan and an extruder as spare!