Leaking Nozzle/Heat Block  

Trusted Member

Hi all, Need some help/advice. I have a just over a year old factory assembled Prusa i3 mk3. I have always had a problem with small black spots on long prints, which I now believe is a leaking nozzle/heat block. Reading on the forum it would indicate a incorrectly assembly hot end. But before tearing it apart I was considering the following options.

1) Heat to 285° Loosing and re-tighting

2) Heat to 285° Remove nozzle clean and re-install

3) Heat to 285° Remove nozzle clean and install New nozzle(maybe be time anyways)

4) Put printer in corner and get a drink

5) Forum recommendation ?

I just order a M7 socket, so I'm doing #4 now. Thanks in advance

Posted : 03/08/2019 12:54 am
Illustrious Member

#4, always #4 ... and even IF you decide #1, do #4 first.

But, read and review the E3D-V6 nozzle replacement guide and the E3D-V6 assembly guide first.  Both documents provide key details to prevent you from doing #1 many times and resorting to #4 afterwards.

It is always wise to get more than one opinion......
Posted : 03/08/2019 1:21 am
Noble Member

Most likely the heat break has gradually unscrewed from heat block. Think of the heat block as a fancy nut that is used to abbut heat break and nozzle together to seal their ends against each other. Nothing actually locks the heat break and cooling fins against rotation. The system relies on tension of nozzle against end of heat break to keep things in place (and sealed).

You will need to do all the work at temperature or else molten filament material will lock things together.

By the book you would take everything completely apart follow the E3D instructions for assembly. You may be able to get away with only a partial take apart and advance heat break into the heat block. 

1. Cut zip locks that hold your heater wires or you may run out of slack

2. Heat to filament temperature and unload filament. Remove fan shroud shift parts cooling fan aside.

3. Increase temp to 285C

4. Use wrench to hold heat block in place

5. Unscrew nozzle completely.

6. Reach into empty nozzle hole and clean out old filament debris with counterclockwise twisting of q-tip.

7. Use wrench to twist heat block 45 degree onto the heat break. (viewed from bottom would be clockwise.) This should advance heat break a little further into heat block.  

8. Hold heat block in its temporary 45 degree position with wrench

9. Install nozzle. It should now impinge against end of heat break a bit sooner. Tension to two fingers tight (still at 285C)

10. Let nozzle temp cool

11. Turn off printer

12. Undo hot end cover and straighten out the entire E3d hotend assembly to bring heat block back into normal alignment. The entire assembly including the cooling fins should be rotated, not just the heat block.

13. Redo zip ties.

Hopefully that does it.

This post was modified 1 year ago by guy.k2
Posted : 03/08/2019 1:34 am
Jiheffe liked
Noble Member

For emphasis.

BE SURE TO UNDO THOSE ZIP TIES! The direction of heat block twist in the above process will otherwise over tighten those wires and snap your heater cartridge and thermistor wires.

Alternative is to rotate heat block in other direction 45 degrees with heat off and hot end cover loose. That increases slack. Retighten hot end cover and when our rotate the heat block it comes out in standard position when you rotate it 45 degrees onto heat break.

Posted : 03/08/2019 1:45 am
Jiheffe liked
Illustrious Member

The nozzle and heat break are the important part of the connection.  The heater block is only a part that the two thread in to, and the torque pressure must be nozzle to heat break

Ideally, but impossible, is holding the heat break and torquing the nozzle to it.  Since the heat break is fully threaded, with no wrench surface to grab, we use the heater block and hope the heat break doesn't spin when torquing the nozzle down.  So the process always starts with the nozzle unscrewed from the heater block 1/4 to 1/2 turn, then tighten the heat break into the heater block until it is in full hand tight contact with the nozzle.  Then the assembly is heated and while holding the heater block torque the nozzle to 3 nm.

The 45 degree spin mentioned by Prusa, and Guy, is advisable when this process has not been followed or it is known the torque process has allowed the heat break to "spin" out of the heater block; but is not always needed.

Ideally tightened, the heat break neck should be flush with the top of the heater block, and the nozzle about 1/4 turn away from the HEX bottoming out in the heater block. 

But I defer to the E3D-V6 assembly as the primary and correct procedure for assembling the E3D-V6 assembly in the Prusa printer.


It is always wise to get more than one opinion......
Posted : 03/08/2019 1:50 am
Jiheffe liked
New Member

Bought a new heatend assembly because I accidentally cut a thermistor wire on the last one. Got the whole extruder put back together and replaced the standard nozzle with the steel 0.4mm nozzle. However, it still seems to be leaky not just at the nozzle (in blue), but above (in pink) as well. Even in some prints, the printer will leave behind what looks like little balls of smooth, melted plastic. Did I break the "heat break" trying to put the new nozzle on it cold? I figured I could replace the nozzle while it wasn't assembled to make it easier. 

Posted : 11/08/2020 7:50 pm
Veteran Member Moderator


It's possible you could have cracked he heatbreak.

if you assembled it cold, you may not have got the nozzle / heatbreak  joint, tight enough

It's hard to see, through the molten filament, but it looks like your nozzle may be hard against the heat block, which usually means the heatbreak is not far enough into the heat block.

regards Joan


I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 11/08/2020 11:35 pm

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