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Nozzle/heater block clogging

Active Member

I'm having a problem with TPU clogging about 1 hour into printing an iPhone case. It lays down 2-3 layers, then no more filament comes out. The printer keeps printing as if nothing is wrong and will complete the print. If I stop the print after the filament stops coming out the nozzle, the filament appears to be ground down slightly where it is fed through the extruder gears, so I know it's getting clogged. After inspecting the nozzle, heater block, and hot end, it appears the clog is in the heater block or nozzle (the hot end is clear). If I print with PLA it completes the print fine.

Here are the specifics:
Filament: NovaMaker TPU 1.75mm, 96A Shore Hardness. I've also tried with Yoyi 1.75mm TPU 96A with the same thing happening.

Printer: Ender 3 with glass bed
I've installed the PrinterMods direct drive mount and the EZR Struder extruder
Nozzle: 0.4mm (I've replaced the nozzle and the same thing still happens)
Hot end: Micro Swiss (I just installed this but also had the exact same problem with the stock hot end)

Slicer: Cura 4.7.1 using the NinjaFlex profile (specifically designed for the EZR Extuder) from CHEP Cura for Creality Printers 4.7.x profile (

Nozzle temp: 228C
Bed temp: 60C
Fan: 100% (on entire time)
Print speed (including initial layer): 20 mm/s
Layer height: 0.12 (I've also tried 0.2 and had the same problem)
Retraction: 0 (I've also tried retraction 1.2 mm and had the same problem)
Line width: 0.4
Flow: 105% (I've also tried 100% and had the same problem)
Infill: 100%

I've tried printing 2 different cases and the same thing happens with both. I examined the Gcode to make sure there wasn't an error where the nozzle temp was accidentally set to 0 midway through, but there wasn't (it stays 228C the whole time). I also changed the nozzle to a new clean one but still happens.

Any suggestions as to what's going on?


Topic starter Posted : 12/11/2020 10:25 pm
Expert Moderator

Hi Adam,

With TPU the big problem is the filament can buckle somewhere in the filament path. I'm surprised your settings actually work as I've had to use drastically different settings than yours on my Bowden-style printers (Creality CR-10 Mini in my case).

I would start by modifying as follows:

Nozzle temp: 220°C
Bed temp: 60C
Fan: 100% (from layer 3 onwards)
Print speed (including initial layer): Initial layer 50%, rest 40 mm/s
Layer height: 0.16mm
Retraction: 7mm
Line width: 0.4
Flow: 105% (I've also tried 100% and had the same problem)
Infill: 20%


Using 100% infill is a recipe for clogged nozzles as even the slightest overextrusion in the extrusion multiplier means the extra plastic has nowhere to go, so the extruder starts slipping/grinding or the filament buckles and blocks. You can sometimes resolve buckled filament by briefly pressing the filament release lever near the extruder (same action you take to load filament). By releasing the pressure from it, the filament will "bounce back" into a straight line (you'll notice the strand in the extruder moves backwards about 1cm as soon as the lever spring is compressed) and this should re-establish normal flow.

Another observation is that your settings promote heat creep as you had a high temperature, and very low print speed and low layer height (which both lead to very low filament flow rate). That means the filament has a greater tendency to stick to the hotend before the nozzle.

Lastly, I needed about 10mm of retraction on my printer to get acceptable reduction of stringing. Your Ender has a slightly shorter Bowden tube than my CR-10 so I've suggested a 7mm value as a starting point. Unlike with rigid filaments, much of the retraction distance is used up un-compressing the filament within the Bowden tube so you'll need to use considerably greater distance to achieve the same effect.

If my settings result in excessive buckling or unwanted underextrusion because the filament slips, reduce the print speed to 30mm/s.

If the problem still persists, look for any area in the filament path where the filament isn't well-constrained and could bend sideways and block. The Creality extruders usually have quite a bit of clearance after the extruder gear and I frequently had buckling in that region. There are a couple of prints you can fit to the area to constrain the filament path better, such as this one - . Many of them are based on having a cut section of Bowden tube shaped very close to the extruder gear; some other designs incorporate the same thing out of plastic; some are a clip-on insert that slides over metal extruders (I use one of those for my Kossel but was unable to find one for my CR-10).

Let me know how it goes 🙂


Posted : 25/11/2020 11:51 am

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