Leaking Hot End?

I think I have an issue with my hot end. I was getting blobs of filament when printing, and when I took off the fan shroud, saw the following:

Do I have to replace the Hot End or just clean it? How do I clean it? Acetone bath?

if you’re are careful you can take it apart hot (but turned off) and all the gunk will come off before it’s cold. this happens when the nozzle isn’t tightened against the heat break inside and the filament squeezes out. careful around the heater and especially the thermister wires they’re delicate and check for shorts before you put it back together.

Don’t understand - hot but turned off… How do I do that? Can I just heat it to about 200 then use a needle or something to flake it off? Once I do that, I can remove and fix the gap, correct?

well, it doesn’t go cold right away. if you short the thermister while tools around those parts while it’s live it could burn the motherboard out. It’s happened to me twice I let it get cold. heated it to 215, turned it off then scraped the plastic off (the first time mine was a large glob that was still cold on the outside) then use your tools to take it apart while the plastic is still molten/soft

You can clean it while it’s on; just do not use a metal wire brush to clean it. I use round tooth picks or BBQ skewers to scrape off the majority of the plastic, then a piece of scrap cloth to finish up.

When you press the Bowden tube into the top of the hot end, it is supposed to go all the way down and rest flush against the top of the nozzle.

You are getting plastic squishing out because any or all of the following are true:

  1. The Bowden tube is not cut at 90 degrees or is not cut cleanly. If it has even a slight taper or a burr at the end the longest piece of the tube will contact the nozzle first and prevent the tube from going in any further. That will leave a gap on the other side which liquid plastic will slowly leak out through.
  2. The nozzle tip has come loose and is not tightened up all the way against the Bowden tube.
  3. The Bowden tube was not pushed all the way in to begin with. Let’s say, for example, that the hot-end was not clean when you last re-assembled it. If a piece of stray, hardened plastic was still in the throat, the Bowden tube may have come to rest against it making you think you had pushed it all the way in, when in fact it was caught on something. The entire path must be clean before you start reassembly.
  4. The fitting that the PTFE tube pushes into at the top is not tight or has backed off somewhat. That will take the tube up with it creating a gap at the bottom.
  5. The fitting that the PTFE tube pushes into at the top has a damaged gripping mechanism and is no longer able to hold the PTFE tube firmly in place and should be replaced.
  6. There is a collar at the top of the fitting that, when pressed down, will (should) release the lock on the Bowden tube to allow the tube to be removed. At some point, something could have pressed down on that collar and released the lock’s pressure on the tube, allowing it to back off. There are clips that fit under the collar to prevent that. You may have lost it.

Awesome explanation! Thanks!

Just 1 more question. I saw a video that the nozzle should NOT be tight against the heat block.

Is that correct?

that’s is correct, if it is then it’s not tight against the heat break. so set the heat break far enough into the heat block that when you tighten the nozzles they can’t quite reach the heat block.

I screw them in by hand and get it hot to tighten with a wrench. then retighten after a print or 2 to make sure.

Oh and after you get it back together make sure your bed is level and check your Z-offset it might be different

So what I saw was about 1 mm or so gap between the nozzle and the block, correct?

The nozzle should not be tight in the heat block.

Sorry if I am asking the obvious questions - still learning!

well 1mm is a lot to me but I always just make sure it stands proud of the block.

So the PTFE tube is what the nozzle is tightened against?

That depends on your parts. on mine, the PTFE tube stops at the heat break and it’s all metal down to the nozzle. if yours has a PTFE tube that goes through then yes the nozzle tightens against that and the fitting at the top that holds the Bowden tube should be tightened last to press the tubes all together inside so no gaps open up.

It’s whatever the CR 10S Pro V2 comes with…

I don’t have an “all metal” hot end, so my advice didn’t factor it in since I’m not used to the procedure that applies to it.

Take your nozzle off. If you can push the Bowden tube all the way through and out the other end, then you don’t have an “all metal” hot end (like mine). In that case I would argue that you DO want to tighten the nozzle to the heat block (no gap). My procedure for installing the nozzle is as follows:

  1. screw in the nozzle and leave a 0.5 to 1mm (or so) gap between it and the heat block.
  2. insert the Bowden tube all the way down until it rests on the nozzle. As mentioned earlier, the Bowden tube has to be cut square and smooth so it contacts the nozzle all the way around the circumference, leaving no gaps.
  3. Tighten the PTFE fitting at the top and insert the collet (collar? not sure what the proper term is).
  4. Heat the hot end to 220C or so but do not run filament through it.
  5. Tighten the nozzle to the heat block. This will compress the Bowden tube against the top of the nozzle which should make a nice tight seal. Tightening the nozzle to the heat block (i.e. metal-on-metal) ensures the nozzle won’t work its way loose. Doing this while the system is hot ensures that thermal expansion won’t work it loose either.

The problem (actually, there are are a couple) with the non-all-metal hot ends is that there’s nothing for the nozzle to press up against, other than the heat block. The Bowden tube, being a type of plastic itself, is flexible and doesn’t supply a secure surface to tighten against and so you can’t really be sure that you’ve sealed off the nozzle just by the feel of it. You can tighten the nozzle to the heat block and still have a gap and not know it until plastic starts slowly oozing out the sides.

With the all-metal heat breaks, as @Glenn says, you can feel the nozzle bind against the bottom of the heat break and so tightness = good seal.

So, unless you already know the answer, do the Bowden tube test. If it goes all the way through, use my method. If it doesn’t, use @Glenn’s.