1 Topic by SvdSinner

  • SvdSinner
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  • From: Ames, IA
  • Registered: 2015-04-27
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Topic: Extruder thermistor

I may be an experienced maker, but as far as 3d printing goes, I'm a newb.

I recently did a print, but didn't put any glue on the bed.  I did other things for 10-15 min, and checked on things.  Since the print didn't stick to the bed, the extruder tip was covered with a small white tentacled hockey puck of extruded filament that it was dragging across the bed, I cancelled the print, and started to clean it up.

During the cleanup, I broke both wires to the thermistor.  sad  (They were the identical color as the dozens of other strings of extruded plastic mess I was supposed to be pulling off.  Cut me some newb slack.  hmm)

I ordered a new 100k ntc thermister since I found posts mentioning it could be replaced, and I'm no stranger to modding electronics.

However, I haven't found anything about how to disassemble the extruder head to get to the thermistor to replace it.

I've removed the nozzle from the extruder, and cleaned it enough to locate the screws, etc.  I haven't yet opened the nozzle cylinder chamber thing, because I'm not 100% sure how to proceed since I assume the chamber is filled with hardened ABS locking everything together.

How do I proceed?

  • I've got butane and  propane micro torches I could heat it with to melt the internal ABS

  • I've got 12V power sources I could hook to the heater and let it melt the blob

Once the blob is melted, what comes apart? 

  • Does the bottom nozzle detatch from the body?

  • Does the throat screw (connects nozzle to rest of extruder detatch)?

Are their any other delicate pieces that I need to make sure I don't damage?
Any critical alignment steps when I reassemble?

2 Reply by jasonb.194 (edited by jasonb.194 2015-04-28 02:08:25)

  • jasonb.194
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Re: Extruder thermistor

Instructions will vary on if you have the new or old style extruder. If the thermistor is on the side, then you have the old style.

Once you take off the extruder. I suggest removing the heater core. Using a small wrench, remove the nut on the heat break. You can use a rod or drill bit in the heater core opening for leverage as well as the nozzle is round.

Once this is removed, you can use a torch to burn out the ABS (if you were just removing a working thermistor, this should wait until after you remove the thermistor. Since your is broken and your replacing it, it won't matter if its damaged further.).

Once the ABS is cleaned out, use a wrench on the flats of the heat break and the drill bit to remove the nozzle from the heat break.

Remove the level sensor using a small screw driver and then the thermistor. On the old style nozzles, the thermistor is secured in by high temp glue and the sensor.

On the newer nozzles with the thermistor on top, you should be able to remove it after separating the heat break and the nozzle.

When replacing the thermistor, make sure to use a heat resistant glue. I have used high temp gasket glue myself and it works well.

3 Reply by SvdSinner

  • SvdSinner
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Re: Extruder thermistor

Thank you!  Big help

jasonb.194 wrote:

Remove the level sensor using a small screw driver

Oh crap.  Level sensor?  I didn't realize there was another component in that assembly that I may have broken.  I was certain their were only 2 wires, and there is only one hole for wires (BTW, I've got a side mounted thermister, so I'm assuming its on old-style)

Where is this level sensor and how do I check it when I get things open?

EDIT:  I just got the nozzle, the heater core and the tube apart.  (My butane torch worked perfectly.)  However, now that I am farther along, I have another issue.  I cleaned out the filament tube easily enough, but the hole where the thermistor goes, I'm not sure how I can get the old thermistor out, or if I've already gotten it out.  With my USB microscope,  I can see broken glass and other detritus from the broken thermistor, but it is really tough to tell what is glass and what is the clear glue they used to seal it in.  I tried for a while prior to the picture to fish it out with picks and hooks to no avail.  I don't know if a drill bit could pull stuff out, or it the glass is too big to be grabbed & pulled out by a slowly rotating drill bit.

For now, I'm soaking the head in acetone to hopefully dissolve the glue. 

Any suggestions?

4 Reply by carl_m1968 (edited by carl_m1968 2015-04-28 01:33:43)

  • carl_m1968
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Re: Extruder thermistor

SvdSinner wrote:

Thank you!  Big help

jasonb.194 wrote:

Remove the level sensor using a small screw driver

Oh crap.  Level sensor?  I didn't realize there was another component in that assembly that I may have broken.  I was certain their were only 2 wires, and there is only one hole for wires (BTW, I've got a side mounted thermister, so I'm assuming its on old-style)

Where is this level sensor and how do I check it when I get things open?

EDIT:  I just got the nozzle, the heater core and the tube apart.  (My butane torch worked perfectly.)  However, now that I am farther along, I have another issue.  I cleaned out the filament tube easily enough, but the hole where the thermistor goes, I'm not sure how I can get the old thermistor out, or if I've already gotten it out.  With my USB microscope,  I can see broken glass and other detritus from the broken thermistor, but it is really tough to tell what is glass and what is the clear glue they used to seal it in.  I tried for a while prior to the picture to fish it out with picks and hooks to no avail.  I don't know if a drill bit could pull stuff out, or it the glass is too big to be grabbed & pulled out by a slowly rotating drill bit.

For now, I'm soaking the head in acetone to hopefully dissolve the glue. 

Any suggestions?


By level sensor he means the silver nub that makes contact with the corner plates on the bed during calibration. That nub is actually a screw that goes through the top of the heater block through half of the hole that holds the thermistor and out the bottom of the block. It is not really a sensor of any kind. Just unscrew it and you will have a normal round hole where the thermistor goes. If it has debris in it just clean it with s small drill bit about yhe same size of the hole. A drill will work fine it will crush and remove the glass before it does any damage to the brass.

Printing since 2009 and still love it!
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5 Reply by jasonb.194

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Re: Extruder thermistor

carl_m1968 wrote:
SvdSinner wrote:

Thank you!  Big help

jasonb.194 wrote:

Remove the level sensor using a small screw driver

Oh crap.  Level sensor?  I didn't realize there was another component in that assembly that I may have broken.  I was certain their were only 2 wires, and there is only one hole for wires (BTW, I've got a side mounted thermister, so I'm assuming its on old-style)

Where is this level sensor and how do I check it when I get things open?


By level sensor he means the silver nub that makes contact with the corner plates on the bed during calibration. That nub is actually a screw that goes through the top of the heater block through half of the hole that holds the thermistor and out the bottom of the block. It is not really a sensor of any kind.


Sorry, this is correct. Its not technically a sensor, but is used to detect the height of the bed when leveling using a small current to check for a closed loop.

As for the glue, I pulled my thermistor out without issue. It has a rubbery consistency and can be removed easily.