Hotend Thermal Runaway after following heatbreak replacement guide.
 

Hotend Thermal Runaway after following heatbreak replacement guide.  

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Brad B
(@brad-b-2)
Active Member

I replaced the heatbreak in my MK3S with a "Genuine E3D V6 Heat Break (1.75mm) V6-175-BREAK" today after reading about the common retraction failures/bulbing of the custom Prusa heat break. 

I haven't had an issue with clogging yet but I'm having issue maintaining 215C when the fan comes on after the first layer. It will hover right around 12-15 degrees below the setpoint until the "THERMAL RUNAWAY" error is thrown and the print stops.

I did a PID tune which may have helped some but I was watching the unit closely and it's still hovering in the danger zone when the fan is at full speed.

I for example did a Calicat print earlier and it failed after the 1st layer. I switched to Advanced more in PrusaSlicer and turned max fan speed to 80% and it completed no problem.

On my current test cube print that is going I watched the thing unable to maintain 215 so I turned the fan speed from 255 to 200 on the LCD screen and it is now maintaining temperature fine.

I've ordered a new thermistor (only $10 thankfully) just in case, but I'm not sure if it's really a thermistor problem.

Is it heat break related? I believe I followed Prusa's instructions on heat break replacement correctly. I didn't use the exact thermal compound they listed (I used Arctic MX-4).

My temperatures seem to stay within +/- a degree just by decreasing fan speed, but I don't see anything different about fan configuration. It's not like you can place the blower motor backwards and you never remove the hotend fan.

This topic was modified 2 months ago by Brad B
Posted : 05/01/2021 4:07 am
Brad B
(@brad-b-2)
Active Member

It appears to struggle to maintain 215C until 2mm off the Z-axis. Is this normal?

Posted : 05/01/2021 5:25 am
JoanTabb
(@joantabb)
Moderator

@brad-b-2

Hi Brad, this is unusual behaviour. 

can you please let us see pictures of your Pinda Probe, hot end and 'part fan shroud' area from the left, right and front please? 

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 : 05/01/2021 12:25 pm
bobstro
(@bobstro)
Illustrious Member

I'd check the alignment of the part cooling fan duct to make sure it's not blasting the heat block instead of the nozzle area. Consider adding a silicone sock to insulate the block from the fan airflow.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 05/01/2021 2:54 pm
towlerg
(@towlerg)
Prominent Member

Do Prusa and E3D v6 use the same thermistor?

Posted : 05/01/2021 3:47 pm
JoanTabb
(@joantabb)
Moderator

@towlerg

the thermistor capsule is the same for e3dv6 from e3d and Prusa, but e3d printers have a connector in the wiring near the extruder, whilst Prusa have an insulated joint in the same place! 

It's a 100K Semitec Capsule NTC thermistor

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 : 05/01/2021 8:02 pm
Brad B
(@brad-b-2)
Active Member

Here's some photos.

 

 

Posted : 05/01/2021 9:23 pm
Brad B
(@brad-b-2)
Active Member

Posted : 05/01/2021 11:26 pm
JoanTabb
(@joantabb)
Moderator

@brad-b-2

In the Bottom picture, the thermistor leads seem to go under the heater. this leaves then more exposed to a Blob of doom than if they go over the top of the heater wires. 
that won't cause a thermal runaway

I don't see anything obvious 

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 : 05/01/2021 11:37 pm
towlerg
(@towlerg)
Prominent Member

Particularly in the first and second pictures, it seems that the part fan is blowing directly onto the heater block?

Posted : 06/01/2021 10:07 am
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