Fix an oozing or leaking heat block

 Fixing an oozing or leaking heat block

Oozing heat blockIf you have done 3D printing, you may have experienced the oozing or leaking heat block problem.  This is where you have filament oozing from the heat block on either the top side by the throat tube, the bottom side by the nozzle or both.  This plastic will start to melt and drip down on your prints, and over time will burn on to your heat block leaving a big mess.  In this section I will discuss why this happens and how you can fix it.

 Why does this happen?

Incorrect block assemblyYou are probably wondering how this happened in the first place.  The main reason is that the heat block assembly became loose at some point.  This may be from movement and vibration when printing, or maybe you had to work on the assembly at some point to clean it or something else.  In the illustration on the right you see that there is a gap between the throat tube and nozzle inside the heat block.  This gap is what allows the heated filament to ooze out.  The heated plastic will be forced through the threads of the throat tube and possibly the nozzle and start pooling up at the top and bottom of the block.  If left long enough, the plastic will run down the side of the heat block and drip onto your nice print.

Now you are wondering, how can there be a gap there?  You say to yourself, I tightened the nozzle in when I re-assembled it, there can't be a gap.  There is something you need to understand about metal.  When it is heated, it expands.  When a metal ring is heated, that expansion will be outwards.  If the throat tube and nozzle are not tightened together enough, the expansion of the block can cause this gap.  

How can I fix this?

So now you are wondering, is this something I can fix, or do I need to buy a new heat block assembly. There is a good chance you can fix this. The main thing is to tighten things when the block is heated and the metal is expanded during reassembly. This will reduce the chance of that gap forming the next time it is heated.

Heat block partsSince your heat block was leaking, you should first disassemble it and clean it.  Clean parts  reduce the chance of leaking in the future.  Remove your heat block assembly from the extruder carriage and set your printer to preheat.  preheating for ABS is probably the best as it will get your heat block to around 240 C (464 F) making things easier to clean.  With pliers holding the heat block, use a wrench or another set of pliers to remove the nozzle.  Once that is removed, your throat tube should come out easily.  Be VERY careful as the parts are extremely hot.  Use a wire brush to clean away any plastic from the throat tube, heat block and nozzle.  You may need to re-heat the parts to clean them good.  Once cleaned, you can begin to put it all back together.

Correct heat block assemblyThese first steps are easier to do when the parts are cool and you can use your hands to fit them together.  The proper way to assemble the heat block is to first thread the nozzle into the heat block, and once it is in all the way, back it off 2 turns.  Next, thread the throat tube in until you feel it hit the end of the nozzle threads.  DO NOT use pliers on the throat tube.  With the throat tube in all the way, grab the heat block with a pair of pliers and use a wrench to tighten the nozzle in place.  Once that is all together, heat up the heat block to temperature while holding it with the pliers.  This can be done with the heater on the printer, or the burner on your stove.  Don't use a torch or it may get too hot.  Once heated, tighten the nozzle a bit more.  This will ensure that the gap between the throat tube and the nozzle will be closed not letting the filament ooze out.  In the illustration above, you will notice that after assembly, the nozzle is still not tight against the heat block.  This will allow you to tighten it again if you need to.  One more thing to note.  Do not put a nut on the throat tube and tighten it to the heat block.  This can cause more issues.  

Now you can re-assemble the extruder assembly.  Correct nut assemblyUse the nut on the throat tube to tighten the extruder assembly to the carriage to prevent the heat block assembly from spinning when printing.  Incorrect nut assemblyBe careful not to over-tighten the nut as you can easily break the throat tube.

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4 Replies to “Fix an oozing or leaking heat block”

  1. After reassembling these pieces described above, due to getting a broken off piece out of the neck, I had a terrible leak top and bottom of the heat block. I took it apart, cleaned (acetone and all) everything up, reassembled it making sure all was very tight this time; however, I still have a smaller leak just under the heat block out of the top of the nozzle so your info about giving it an extra tightening after reheating it just might work. Great diagrams! I will try it again, but think I will not reclean the cold plastic as it will just melt away, I hope, anyway. It was a job before as I had to take so much apart, then my calibrations for the axes had to be reset. It tries the patience of a 70 yr old lady!! By the way, my throat tube comes with a white plastic lining inside that was supposed to act like a washer at the junction of nozzle and throat tube.

    1. You say that you removed a broken off piece. Where was the piece broken from, the throat tube? If it was, you will need to replace the throat tube. If the end is jagged, it will just leak again even if you tighten it. The end of the throat tube needs to be smooth because it mates with the smooth end of the nozzle to create the seal that prevents it from leaking. The reason you tighten it while it’s hot is because if you don’t, the heat expansion of the heat block will separate the throat and nozzle causing it to leak again. I would heat the block to about 240c at least when tightening it together. Remember, NEVER grab the throat with pliers.

  2. Thanks for your reply. The piece from the throat tube was high up above the heat so wouldn’t melt. When I took all apart I soaked all parts in acetone. Then the piece was able to be pushed out easily. I have just cleaned the nozzle again (second time) in acetone. I forgot to say that the last time I disassembled it a small almost circular piece of metal , very thin, came away, not sure if off the nozzle or the throat tube. I suspect the nozzle as I also have noticed rust on the neck of the nozzle. Odd when it should be brass. I may need to buy a new nozzle. I did grab the throat tube in the middle only to tighten it when replacing into the extruder. How else does one tighten it enough? I also notice you have two nuts to tighten. Mine only has one that came with it. I used it at the top of the heat block, not under the extruder carriage which was how it came assembled in the kit. I will add one more when I get a new nozzle.

    1. You said ” I did grab the throat tube in the middle only to tighten it when replacing into the extruder. How else does one tighten it enough?” If you read the BLOG post it tells you how to tighten the nozzle to the throat tube. You never grab the throat for two reasons. First and foremost, you will mar the threads making the nut hard to move. Second, the thin wall of the tube makes it easy to break. Grabbing it with pliers can crush or break the tube.

      You also said “I also notice you have two nuts to tighten.” The pictures are just ones I found on a google search. Mine only has one nut. Tightening the nozzle to the throat tube is how those two get locked into place which is why the nut does not go against the heat block. Another reason is that with that against the heat block, it is one more thing that is going to heat up making your preheat time longer. The nut is to tighten the throat tube to the carriage to prevent it from spinning when the carriage is moving. If the throat spins even a little bit while printing, that will change the height of your nozzle mid print and you DON’T want that. You would get anomalies in your layers wherever the tube spun. Because of all of this, there is no need for you to add a second nut.

      Also, tightening the nozzle to the throat while it is hot is another key ingredient. Heat will expand the aluminum block. Because of this, if the nozzle is only tightened when it is cold, the heat expansion of the block will cause the nozzle to loosen its grip on the throat tube creating a gap for filament to leak from. Part of the reason for the whole article.

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