<p>Most of the time I print PLA with my Anet ET4 (with Marlin firmware). Yesterday I again wanted to print with ABS and preheated nozzle (245 °C) and bed (80 °C). Everything worked fine for a few minutes, but suddenly I got an error:</p>
<blockquote>
<p>Thermal Runaway: Bed</p>
<p>Printer Halted</p>
<p>Please Reset</p>
</blockquote>
<p>I reset the printer and after booting (Anet logo was shown), this thermal runaway error immediately popped up again. I then removed the NTC thermistors of the bed and also of the print head with no improvements.</p>
<p>I read that in this case, I should check the cables and the thermistors - but they are all good, the same problem despite replacing the cable.
I also do not understand why this error occurs immediately after booting.
Maybe could it be that a MOSFET on the board is defective?</p>
<p>I hope someone can help me with this problem.</p>
<p><a href="https://i.sstatic.net/gUeAl.jpg" rel="nofollow noreferrer" title="Failure screen"><img src="https://i.sstatic.net/gUeAl.jpg" alt="Failure screen" title="Failure screen" /></a></p>

CC BY-SA 4.0
2022-06-14T22:01:33.607Z
How did you test the bed thermistor? From this description I would guess that the bed thermistor reports an invalid temperature.
Lars Pötter
CC BY-SA 4.0
2022-06-16T08:59:57.683Z
It has been tested with a multi meter (normal resistance measurement).
I even do not get into the home menu because the error message appears immediately after switching on. Tried also other 100kOhm NTC thermistors and also a print bed of a Anet A8 with no improvements.

With my little knowledge in 3D printing I can't imagine why the mainboard of the printer could be broken!? And before I buy a new mainboard I will check all other error sources to be on the save side.

I appreciate any advice.
w31x
CC BY-SA 4.0
2022-06-17T16:02:13.277Z
The issue might be between the connector for the bed sensor and the pins of the processor. You could check the PCB for bad solder joints. There are probably some resistors between the connector and the processor.  The voltage measured at the processor pin should be above 0V and below 5V. Probably rather close to 0V so more like 1V or less.
Electronics can break, this is not 3d printing specific. But your printer is neither open source software nor open hardware. That makes i hard to give specific advice.
Lars Pötter
CC BY-SA 4.0
2022-06-18T13:27:27.427Z
OK, I will try it.
Should this error also occur if no sensors (thermistors) are connected? Because if I disconnect the printbed and also the hotend, I still get this thermal runaway bed error immediately after turning on the printer. Is this normal for a working motherboard too?
w31x
CC BY-SA 4.0
2022-06-19T21:34:33.160Z
yes with the thermistor not connected the error must occur! One of the failure modes of the thermistor is that the cable breaks and that looks for the electronics exactly the same as no thermistor connected.
Lars Pötter
<thermal-runaway>
Anet ET4 - Thermal Runaway immediately after Boot
w31x
# Anet ET4 - Thermal Runaway immediately after Boot

(Asked by: username_0 on 2022-06-12)

Most of the time I print PLA with my Anet ET4 (with Marlin firmware). Yesterday I again wanted to print with ABS and preheated nozzle (245 °C) and bed (80 °C). Everything worked fine for a few minutes, but suddenly I got an error:

> Thermal Runaway: Bed
>
> Printer Halted
>
> Please Reset

I reset the printer and after booting (Anet logo was shown), this thermal runaway error immediately popped up again. I then removed the NTC thermistors of the bed and also of the print head with no improvements.

I read that in this case, I should check the cables and the thermistors - but they are all good, the same problem despite replacing the cable.
I also do not understand why this error occurs immediately after booting.
Maybe could it be that a MOSFET on the board is defective?

I hope someone can help me with this problem.

[![Failure screen](https://i.sstatic.net/gUeAl.jpg "Failure screen")](https://i.sstatic.net/gUeAl.jpg "Failure screen")

**Tags:** thermal-runaway

> **Comments:**
> **username_1**: How did you test the bed thermistor? From this description I would guess that the bed thermistor reports an invalid temperature.  
> **username_0**: It has been tested with a multi meter (normal resistance measurement). I even do not get into the home menu because the error message appears immediately after switching on. Tried also other 100kOhm NTC thermistors and also a print bed of a Anet A8 with no improvements.  With my little knowledge in 3D printing I can't imagine why the mainboard of the printer could be broken!? And before I buy a new mainboard I will check all other error sources to be on the save side.  I appreciate any advice.  
> **username_1**: The issue might be between the connector for the bed sensor and the pins of the processor. You could check the PCB for bad solder joints. There are probably some resistors between the connector and the processor.  The voltage measured at the processor pin should be above 0V and below 5V. Probably rather close to 0V so more like 1V or less. Electronics can break, this is not 3d printing specific. But your printer is neither open source software nor open hardware. That makes i hard to give specific advice.  
> **username_0**: OK, I will try it. Should this error also occur if no sensors (thermistors) are connected? Because if I disconnect the printbed and also the hotend, I still get this thermal runaway bed error immediately after turning on the printer. Is this normal for a working motherboard too?  
> **username_1**: yes with the thermistor not connected the error must occur! One of the failure modes of the thermistor is that the cable breaks and that looks for the electronics exactly the same as no thermistor connected.  

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## 0 answers

