BED THERMAL RUNAWAY - How to recover, how to fix? – Hardware, firmware and software help

rogerinhawaii

(@rogerinhawaii)

Estimable Member

BED THERMAL RUNAWAY - How to recover, how to fix?

I was two hours into a four hour print and the print just stopped with the error message "BED THERMAL RUNAWAY". The temperature shown was way too high, and I watched it slowly dropped down to around 30 degrees centigrade, although the bed never seemed excessively hot to the touch. But then nothing happened. I figured there would be a RESUME option but there isn't. Has it simply aborted the print completely?

Should I turn the machine off and back on again? Is there any way to resume the print? Do I just have to throw this print away and start again?

I searched around for "BED THERMAL RUNAWAY" and most advise looking for a loose connection or broken wires but I really have no idea specifically what parts and where on the machine they're referring to. Perhaps people with years of experience with printers and electronics in general can understand the very short answers, but that's not me. Some diagram or photo would really help to show me what I should be looking for to fix this. How, really, do I proceed at this point? How do I diagnose the cause? Do I just try again and see if it works?

Posted : 07/05/2020 3:23 am

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

NO RESPONSES?? This is a serious problem. It has now happened TWICE. How do I fix it???

I searched around the web including the PRUSA website forums and the indication is the the software that runs the printer displays that message, and aborts the print, when it detects a sudden DECREASE in temperature that lasts for fifteen seconds. They indicate that one of the possible causes of the temperature drop can be from an air conditioner placed too close to the printer. That's certainly not my particular situation.

They also indicate that a failing temperature sensor (on the bottom of the bed) or a broken or disconnected wire from that sensor can mean the software can't read the temperature or gets fault readings. OK, that would make the software THINK that the bed is cooling down too far (it needs to be at about 210 degrees in order to hold on to the print), but that doesn't mean a thermal runaway. It would only runaway if the software ignored the sudden temperature drop and kept the heater element on the bed turned on. So at the very least the message should be TEMPERATURE MEASUREMENT PROBLEM not THERMAL RUNAWAY.

I would expect that the software would PAUSE the print and spend some time checking the temperature to see if it (soon?) gets more reasonable measurements, just as it seemed to be doing when I heard the beep and could see the temp values slowing dropping from 210 to normal. It SHOULD be able to recover all by itself if indeed it was a spurious reading or temporarily faulty connection.

And on top of all this the posts on the forums don't really explain in sufficient detail how to resolve the issue.

Posted : 08/05/2020 12:33 am

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Edward Clark

(@edward-clark)

Active Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

Commenting so I can follow...

Posted : 08/05/2020 12:54 am

rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

UPDATE

I ran the same print again. It started off just fine. The bed temp started at 215 degrees for the first layer then went to 210 for all subsequent layers, just as expected. The print head temp was 60 degrees. After about a half hour of printing I noticed that the head temp fluctuated a bit, from the normal 60all the way don to 49, but then it got back to 60 ad stayed there for a while. But THEN, the head temp plummeted, over about a minute's time, to 38 degrees, and that triggered the BED THERMAL RUNAWAY message and the print aborted.

Both of the print head fans were on the entire time, and even stayed on after the print aborted, A few minutes after the abort the fan on the left side of the print head shut down, but the fan on the front (the one's that at a 45 degree angle) never stopped running.

So, first of all, this is clearly NOT a BED THERMAL RUNAWAY. I had previously checked out, as best I could, the temp sensor and cabling on the BED and that all looked fine. The problem is with the PRINT HEAD. It also appears NOT to be a problem with the temperature sensor on the print head, either it not working or there being some break in it's wires. MAYBE the print head HEATER is failing. But how do I diagnose and fix THAT?

I need a solution to this problem right now. I've successfully printed out six of these objects and need 30 more to complete my project.

I also see that the print is not very good. The front of this object should be nice and smooth, as it has been with numerous other prints for this same object and the same print settings. But you can see that there are horizontal ridges across the front surface. I have no idea if this is related to the HEAT problem, but maybe...

Posted : 08/05/2020 3:23 am

rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

UPDATE to the UPDATE

I had been watching the temperatures on the PRUSA's display, which looks like this pic. There are icons to the left of the temp readouts. The upper one looks to me like a thermometer. The lower one looks to me like it's indicating the letter H, which I took to mean the print Head, leaving the other one to indicate the print Bed. But apparently the upper one is intended to LOOK LIKE the print HEAD and the lower one to LOOK LIKE the print BED.

The prints that have reported the BED THERMAL RUNAWAY never had any problem with sticking to the bed. I DID have a bed-sticking problem a while back with one other print but it never reported the THERMAL error.

So I guess it IS a bed problem. I had been planning, today, to disassemble the print head section and try to figure out what was wrong with IT, but obviously it's not the head but the bed that has the problem. The things is, I already checked that out yesterday and couldn't find any wire connection problems. I have no clue as to how to diagnose the bed heater and temperature probe themselves.

I could still really use some advice.

Posted : 08/05/2020 7:01 pm

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Edward Clark

(@edward-clark)

Active Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

@rogerinhawaii

Did you try starting a chat session from their website? They are pretty responsive. Might take 20 minutes but they seem to get to you.

This post was modified 5 years ago by Edward Clark

Posted : 08/05/2020 7:44 pm

karl-herbert

(@karl-herbert)

Illustrious Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

@rogerinhawaii

BAD THERMAL RUNAWAY indicates in most cases a broken bed-thermistor wire, not nozzle-thermistor wire. Manually heat the bed to 60degrees and repeatedly move the y-axis back and forth. If the thermistor cable has a loose contact, you can observe the temperature fluctuations on the LCD display. You may have to replace the thermistor cable including the thermistor.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 08/05/2020 8:45 pm

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

@karl-herbert

I tried what you suggested. I repeatedly moved the bed back and forth, slowly, quickly, intermittently, and no effect on the temperature readout. I even jiggled the cable that connects the bed to the control board a bunch. Nothing. The readout stays rock solid at 60 degrees.

I tried another long print and about four hours into the print I get the THERMAL error again.

Posted : 09/05/2020 4:54 am

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

UPDATE:

I did three half-hour prints in a row, keeping a close eye on the printer. The first two went fine. The last one almost didn't finish. There is a small red LED that's on whenever the bed is being actively heated. It's usually blinking on/off quite consistently, indicating to me that it's really trying hard to keep it right at the 60 degree mark. At one point I noticed that the temperature was going down, from 60 to 59, to 58, etc. More importantly I noticed that the red LED was completely off. It got all the way down to 50, with the LED still off. But it then was finished with the print.

I started up another print. It started, as it always does by pre-heating the hot end and the bed, but this time it did the hot end first, with the red LED off, while usually both the bed and hot end are heated up at the same time. Finally the LED came on and I could see the bed temp going back up to 60. It started printing, but then the LED went off again and the bed temp started going down. I "flicked" the connector (that connects to the back edge of the bed and holds the wiring for the thermistor as well as the LED) and the LED came on and the heat went back up to 60.

So, there's something that's causing the bed heater to not come on occasionally (and NOT an issue with the temperature SENSOR). It SEEMS to start mis-behaving mostly after a long print or a series of shorter prints, i.e. after the bed heater has been in use for an extended period of time.

My next plan is to again remove the bed but this time also unscrew, disconnect, examine, and reconnect the thermistor connector that attaches to the edge of the bed.

I sure hope this works.

I've also ordered a replacement thermistor from PRUSA in case it finally appears that the thermistor itself has one (intermittently) bad.

Posted : 09/05/2020 8:26 am

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

UPDATE : SOLUTION ? :

I may have finally figured out the problem. I removed the bed and opened up the connector at the edge of the bed to reveal the ends of the wires that provide power to the heating elements of the bed. The ground wire was just a little bit loose. The washer could move slightly. I tightened it down firmly, reassembled everything, and ran a SUCCESSFUL 6 hour print.

I don't know if this bolt came loose over time or I just didn't tighten it sufficiently when assembling the kit. I often take the approach, when handling multiple bolts on some part, of first lightly installing them all and then going back and tightening them all down one at a time, much as you're supposed to do when tightening bolts on the rim of a wheel. So it's possible that I loosely screwed in the bolts but then failed to properly tighten one of them.

I sure hope this is what was indeed causing the problem I was encountering, basically the heating element just not coming on to keep the bed properly heated. I've got a whole bunch of really long prints to do. So, we'll see.

BY THE WAY... I tried to upload an image to include with this posting and kept getting an HTTP error reported. I tried a bunch of different images to upload and none of them succeeded, all reporting that HHTP error. It seems that there's something wrong with the website today.

Posted : 10/05/2020 6:10 pm

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

Posted : 10/05/2020 6:12 pm

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Edward Clark

(@edward-clark)

Active Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

I suggest you find that step in the manual where it has you tighten those and put a comment on the webpage so that other people that follow behind you can learn from this. Glad to hear you solved your problem.

Posted : 10/05/2020 6:18 pm

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rogerinhawaii

(@rogerinhawaii)

Estimable Member

Topic starter answered:

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

Posted by: @eeclark

I suggest you find that step in the manual where it has you tighten those and put a comment on the webpage so that other people that follow behind you can learn from this. Glad to hear you solved your problem.

Good idea. I just did that.

Posted : 10/05/2020 6:47 pm

karl-herbert

(@karl-herbert)

Illustrious Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

@rogerinhawaii

Thanks for the feedback. Since a relatively high current of about 6A flows over this connection, I would pay attention to clean and well fixed contacts.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 10/05/2020 7:11 pm

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Edward Clark

(@edward-clark)

Active Member

RE: BED THERMAL RUNAWAY - How to recover, how to fix?

@rogerinhawaii

I wonder if the comment has to be approved before it is posted. I just checked 7. Heatbed & PSU assembly (Silver PSU)-Step 4 and didn't see it yet.

https://help.prusa3d.com/en/guide/7-heatbed-psu-assembly-silver-psu_33512

Nevermind... I see the comment on the Black PSU step 4. https://help.prusa3d.com/en/guide/7-heatbed-psu-assembly-black-psu_31936

This post was modified 5 years ago by Edward Clark

Posted : 10/05/2020 7:36 pm