Unresolved Termistor problem?!

I've got one Robo3D R1 (bought in Summer 2014), on the printing head assembly, there are 4 pairs of wires:

- one for the small fan (that I've never seen working since the first printing);
- two common diameter wire pairs (red and black) for termistor and for the "inclined" fan
- last one for the heater (thicker wires).

After about 10 prints I've had many troubles with the extruder I had to disassemble and clean it three times.
Some days ago after the fourth cleaning procedure I had connected every wire and one minute after turning on ther heating head and heating bed a lot of white smoke came from the head. The black plastic cover was full of melted plastic (blue PLA that came almost black), heater and termistor got "glued" to aluminium block.


I've disassembled everything again and had to destroy black plastic cover in order to heat the alumium block to "unglue" the termistor and the heating element.
Then I've connected everything again and using Repetier Host as software I've realized two strange things regarding to similar diameter wire pairs for the fan and termistor:

A - When I connect in some way it Repetier Host shows the information on picture below and:
-> the fan works
->no icon of heat bed appears.
->no XYZ moves are possible using correspondant buttons on Repetier GUI



B - When I connect the opposite way Repetier Host shows the information on picture below and:
-> the fan doesn't work even if I hit the "Fan" button
-> XYZ moves are possible (it works).
-> Heat bed icon appears and works.



Not being an electronics expert there are some things that are confusing me.

If connections on configuration A are the correct how I cannot get fan working as long as Arduino should sense resistance and translate it to temperature (termistor) and not inject current to that connection.
If connections on configuration B are correct how I cannot get fan working?

Is it a termistor problem?

As I've already ordered termistors (it's something very cheap) to replace (NTC 100k) from a ebay Spanish seller (http://www.ebay.co.uk/itm/161580236853?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT).
If you confirm the termistor problem are they compatible? Is there the need of changing something in firmware due to termistor model?

Please help me troubleshooting the problem.

 

I forgot to attach pics about the actual condition of printing head, here they are:

 

THink this turned into kind of a rant. I want to do some work on my hot end wiring etc and dealing with that now crusted with black ash junk pisses me off. at the same time, I worry that taking it apart again will be the last time it comes apart.


I have found this "hot" tightening to be probably bunk to a great extent but I've kept my mouth shut because rarely is a forum a friendly place for dissent.
It doesn't make much sense. I think some classroom engineer is imagining the block expanding hot will somehow have a positive effect on stopping the leak? Threads have never stopped leaks. Its not their job. In this case, the tolerance between nozzle and tube end are the mating parts. They need to be squished together.
I've found that its really just a matter of tightening well. Believe me, I have take that thing apart far too many times. Ensuring that you're tightening the nozzle against the "hexagon" and not against the block. Screw the hexagon in as far as you can while still being able to put a wrench on it. then screw in the nozzle. There should be a bit of a gap between t he nozzle and the heater block when it starts getting tight. Do this stone cold and when it heats up the tolerance will be even smaller. Do it hot and it almost guarantees it being loose when cooled.. aka operating temp. Not to mention just burning your fingers, having a bad time. Forget that.
Put a wrench on that little hexagon tube part and you'll strip it. just tighten the hot end against it using a wrench on the heater block and the nozzle.

It really comes down to poor engineering of the nozzles on these things. Looks like a case of desktop engineering or like the prototype "proof of concept" got mass produced. Oh.. it did? that explains it. Cost of doing business on the cutting edge right? It doesn't actually cut mustard.
I haven't been involved with any of the high end printers, but I can't imagine one of the pretty boxes has anything like this nozzle. I've actually ordered a couple others to see what I can do to get rid of this hexagon.

I would love to hear why one would tighten something like this HOT to get it to stop leaking. I've tightened things at operating temp to ensure they were loose enough at temp.. not the other way round. I get that "hexagon" people say that. But... isn't that just a group of people in a garage? In china?

 

And this is why we apply a certain torque to heat cycling objects. Create enough drag on the threads to prevent them backing out with thermal expansion and contraction cycles. This is how your wheels and cylinder-head stay on, despite great thermal deltas.

I'm reading this and I understand the idea, I just think its going in the wrong direction. I know my anecdote is not proof of anything, until i go through a few dozen of these using the same process. My sample is just too small.

I understand there are at least 2 probably 3 types of metal here... and that never goes well with heat cycling. My experience would tell me to torque cold. And its working.. possibly.

What is missing is well.. first, a breakthrough design. second... a gasket betwixt these parts. they aren't of a finish or material to be joined directly.
Furthermore, a gasket could insulate the hot end from the tube. I imagine that was the thinking behind the ptfe tubes.

 

Briefly reading this it has to do with the different themal expansion coefficients in play. You have brass nozzle, stainless heat break, and aluminum heater block. This means when it's hot you tighten it down to compress the threads and the flats between the nozzle and the heat break. When that cools the materials retract at different rates and stay locked together. Thus when you reheat it returns to the same tensioned position as before, never loosens.

There are designs with a solid nozzle/heatbreak, such as the prometheus. I'm not certain on the design though

 

The main problem (the one in the first post) happened after the adjustment that you point. I've counter-tighten both parts to ensure no leakage could occur. I've also noticed that during the adjustment that thermal break i.e. steel part inside finned aluminium body slightly around aluminium body, something that in my point of view shouldn't happen.
Thank you for the help. Right now I'm focused on electronic fail rather than thermo-mechanical problem. About leakage I think that I'll go into a different hot end, probably E3D v6.
Is the bowden version suitable for Robo3D? There are some comments here that direct is preferred but what are the differences in what concerns to install it on a Robo3D R1?

 

Is anyone interested in troubleshooting my original question? Sorry to say that but a lot of discussion was made around a secondary problem.
Should I open a new Post?

 

The hot end fan absolutely needs to be running. If it's not it could have failed. Give me a chance to read over this and I'll post more here in a bit

 

I can recognize that original post is a bit long but in short I need to know exactly how to assure I'm using the correct cables in the connection between main extruder fan (the bigger fan that is behind extruder) and termistor. It seemed that I've changed that connections but according to my first post pictures it's not clear to me waht is the correct connection schema.

 

The thermistor you linked will work fine. It might be a bad thermistor or it could be a loose connection.

Whatever the case don't run it without a working parts fan

Measuring the resistance is the best way to determine which wire goes to which.