hotend thermostat issue

[MagicEngineer]

I recently began having a lot of failed prints where printing would stop about 45 minutes to an hour in. I had been printing from the SD card so was unable to see exactly what caused this. I did a print through the usb this morning to see what was going on and was surprised to see that the extruder temperature at the time of failure was showing 273c. Since it was only set for 245c, my first thought was that somehow the firmware let it run away with the temp, but now as I am sitting here with the hot end fully cooled it is still showing 273c-275c, This leads me to believe that the thermostat is defective. My question is this. Is this common? this hotend is only about 4 months old.

[MagicEngineer]

I am also now getting an error when I try to jog controls. "printer stopped deu to errors. Fix the printer and use M999 to restart! (temperature is reset. Reset it before restarting)" What is M999?

[Tim]

I am sitting here with the hot end fully cooled it is still showing 273c-275c, This leads me to believe that the thermostat is defective.

Seems unlikely, for the reason that the value you're seeing for the temperature is the same value that is used to close the loop on the temperature control. So if your board is reading 273 degrees and the temperature is set to 245, then it should have the heat completely turned off to try to pull down the temperature.

Possibilities include: Really bad PID values (temperature is aiming for 245 but has a settling time measured in tens of minutes or more) (which is unlikely, unless you inadvertently modified all the PID values), or the board is doing its own thing and is ignoring you; that's possible if there are embedded temperature controls in the gcode. Possibly the gcode has told the extruder to go up to 275?

[Slipshine]

I had one do this is was just a bad thermistor.

[PcS]

I'd vote for bad thermistor.

[MagicEngineer]

I had one do this is was just a bad thermistor.

I believe you are correct. With the thermistor plugged in and hotend fully cooled it registers over 270c and none of the controls respond. With it unplugged it registers 0 and the controls still don't respond. As a test I put a 1k ohm resistor in the plug and it registered 174c and all of the controls work correctly. My fear was that the board was going bad, but this test seems to alleviate that fear.

[Tim]

I'd vote for bad thermistor.

Okay, yes, I guess what happens is that it just keeps reading 270C (although I don't know why, exactly; I thought most thermistors just start getting flaky and getting intermittant readings when they go bad). The controller thinks the temperature is too high and keeps the heater turned off, and eventually it cools down to room temperature. It's a good thing that it doesn't read a wrong low temperature, or you'd end up in thermal runaway until something fried.

For something that is just a block of semiconductor between two wires, thermistors seem to have weirdly complicated behavior when they go bad.

[PcS]

I had one short to ground and it read high. One that would read ok then min temp without any printer movement. They can be flaky.

[creativedex]

Are any of you guys having issues with your thermistors going out every 3 to 6 months? Thats about as long as they last for me. Mine just get flaky and cant hold the temps well but generally its been staying within 10c of the set temps... sometimes i can get away with it for a while but others it just gives me ugly prints... been having buying extra thermistors as often as nozzles. Where are you guys finding these metal nozzles?

[MagicEngineer]

Are any of you guys having issues with your thermistors going out every 3 to 6 months? Thats about as long as they last for me. Mine just get flaky and cant hold the temps well but generally its been staying within 10c of the set temps... sometimes i can get away with it for a while but others it just gives me ugly prints... been having buying extra thermistors as often as nozzles. Where are you guys finding these metal nozzles?

I am starting to realize that the entire hotend should be considered a consumable part. You will wear all of its parts out and you will be replacing them. some more regularly than others. As for the steel nozzles, I got mine by ordering the brass v4 nozzle and requesting the stainless steel in the notes section. Of course at the time it was mentioned on this forum that they only had a few left so it might be worth contacting them and asking if there are any left.