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Thermistor only goes to 90°C (thermal runaway)  

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Sejl
 Sejl
(@sejl)
Active Member
Thermistor only goes to 90°C (thermal runaway)

Hi,

I have had some problem with failed print. It was pulling on a thermistor cable so it was connected only by one wire (between thermistor and black cable). Hotend temperature reading on the display was around 20°C, but the heater was trying to reach 210. Good thing I was around when this happened, so I have prevented more serious damage.

Then I purchased hotend thermistor (order reference: 2121727467), and now hotend temperature goes only up to around 90°C while heater is still trying to reach 210.

Do you have any idea what is going on?!

 

Best regards

Posted : 14/04/2021 10:58 am
Sejl
 Sejl
(@sejl)
Active Member
Topic starter answered:
RE: Thermistor only goes to 90°C (thermal runaway)

Resistance measured at the room temperature is around 110k, and when the hotend starts warming up it quickly goes down to 1-2k, and quickly after that hotend starts fuming. Display now shows around 60°C. My guess is that main board is at fault.

Printer is i3Mk3s

Any ideas?

 

Best regards

Posted : 15/04/2021 7:27 am
Clarmrrsn
(@clarmrrsn)
Honorable Member
RE: Thermistor only goes to 90°C (thermal runaway)

You could have a look at these documents to see if you can find anything, does sound like it may be the board, but would run through the multimeter tests, you may have burnt out the heater as well.

https://help.prusa3d.com/en/article/multimeter-usage_2117/

https://help.prusa3d.com/en/article/thermal-runaway-temperature-drops_2131

All else fails I would suggest contacting prusa via Estore chat, they wil diagnose for you further and hopefully send you the required part under warranty (If it is covered)

 

Tank you very much!...
Posted : 15/04/2021 9:24 am
Sejl
 Sejl
(@sejl)
Active Member
Topic starter answered:
RE: Thermistor only goes to 90°C (thermal runaway)
Posted by: @clarmrrsn

You could have a look at these documents to see if you can find anything, does sound like it may be the board, but would run through the multimeter tests, you may have burnt out the heater as well.

https://help.prusa3d.com/en/article/multimeter-usage_2117/

https://help.prusa3d.com/en/article/thermal-runaway-temperature-drops_2131

All else fails I would suggest contacting prusa via Estore chat, they wil diagnose for you further and hopefully send you the required part under warranty (If it is covered)

 

Hi,

Thank you for your reply.

As I stated in previous message, multimeter test show that thermistor is giving proper reading. For your other point, I'm sorry but I have no idea how can burnt-out heater, that reaches smoking point, influence thermistor reading. Please, if you can, explain in more details.

I have already sent email for warranty fix, but I'm also curious as an experienced engineer what could have caused this thermal runaway (apart from board malfunction).

Thank you again!

Best regards

Posted : 15/04/2021 2:37 pm
Louie Beardell
(@louie-beardell)
New Member
RE: Thermistor only goes to 90°C (thermal runaway)

@sejl

Just had this same exact problem except mine only goes to 140. I was thinking it was the board too but prusa hasn’t responded to me yet.

Posted : 16/04/2021 3:20 am
Sejl
 Sejl
(@sejl)
Active Member
Topic starter answered:
RE: Thermistor only goes to 90°C (thermal runaway)
Posted by: @louie-beardell

@sejl

Just had this same exact problem except mine only goes to 140. I was thinking it was the board too but prusa hasn’t responded to me yet.

No answer for me too. I will wait until monday, and then ask via chat.

Hope you get your response too in the meantime 🙂

Edit: btw, if the printer were not in warranty, I would have already seen what the problem is directly on the board, but since it is still in warranty, I will not touch it just in case.

Best regards

This post was modified 5 months ago by Sejl
Posted : 16/04/2021 3:26 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member
RE: Thermistor only goes to 90°C (thermal runaway)

@sejl

My thinking was as follows.....

If you had a pulled/broken thermistor cable, then heater cable could also be damaged.

At this point as you do not know what the cause is I would not rule anything out, takes 2 minutes to test the resistance of the heater, this could save a lot of time as if you fit for example a board and the heater is still faulty then still have a down printer.  I never assume a part it good until it has been tested.

I assume you replaced the thermistor with the correct Prusa V6 thermistor, not a compatible part?

You are far quicker and easier going through the chat on the EShop, it is a 24/7 service.  Email can take a while for response, normally 5 mins to get through on the chat, you will get live support and troubleshooting for warranty issues.

Good luck.

Tank you very much!...
Posted : 17/04/2021 9:41 pm
Sejl
 Sejl
(@sejl)
Active Member
Topic starter answered:
RE: Thermistor only goes to 90°C (thermal runaway)
Posted by: @clarmrrsn

@sejl

My thinking was as follows.....

If you had a pulled/broken thermistor cable, then heater cable could also be damaged.

At this point as you do not know what the cause is I would not rule anything out, takes 2 minutes to test the resistance of the heater, this could save a lot of time as if you fit for example a board and the heater is still faulty then still have a down printer.  I never assume a part it good until it has been tested.

I assume you replaced the thermistor with the correct Prusa V6 thermistor, not a compatible part?

You are far quicker and easier going through the chat on the EShop, it is a 24/7 service.  Email can take a while for response, normally 5 mins to get through on the chat, you will get live support and troubleshooting for warranty issues.

Good luck.

Thank you! I have checked everything in the meantime. Heater is fine 🙂 Thermistor was purchased directly from Prusa (hence the order number, if anyone of the Prusa team reads this forum). I even purchased two thermistors, and check them one after the other with same result.

Tomorrow, I will contact Prusa team via chat.

Best regards

Posted : 18/04/2021 4:34 pm
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