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Thermal Runaway Error/Bed Preheat Error  

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Robert Crane
(@robert-crane)
Eminent Member
Thermal Runaway Error/Bed Preheat Error

Just overnight, I was printing an object that requires a great deal of retractions and carriage manoeuvres. After everything worked fine for several hours, I had checked the printer and had found out that it had a “thermal runaway error” message which had occurred sometime within a couple of hours before I had checked it previously. This is just the latest issue after having many others beforehand (but not heatbed related, previously replaced print fan support, print fan, hotend and several hotend thermistors. Even though the definitions of thermal runaway are related to the thermistor in the bed, this didn’t appear to be the case as there was a positive temperature reading on the lcd display for both the bed and hotend thermistors. So, without thorough inspection, nothing physical seemed to be wrong.

I then reset the printer and selected a small print job from the sd card to see what the printer would do. Everything seemed to work fine except the bed wasn’t heating up, the temperature stayed constant. The printer is in an enclosure and the room was warm. No drafts from open windows or an air conditioner can get to the printer where it is. Both the hotend and bed temperatures read 24C at the time.  Anyways, after the hotend heated up, I got a “bed preheat error” and the printer halted.

Shortly after this, I took a hair dryer and blew hot air onto the heat bed, the temperature rose rapidly, indicating that the thermistor is still fine or at very worst, has a minor issue (loose, tiny internal wire break etc.  Though these are a bit of work to replace, I do have a spare bed thermistor if need be.

I have had this printer for four months and this is my very first heatbed related issue. If it’s not the thermistor it’s self, what else could it be and why would it suddenly stop working?

I only noticed one thing slightly different about my last print job is that the first line of filament that comes out at the beginning was in a slightly different place then usual on the plate but it wasn’t much and I thought nothing of it as this had happened to me at least once before and nothing went wrong previously related to that. The only other adjustment that was made is that I had raised my live Z because my nozzle appeared to have been a bit too low during my previous print judging from it’s cosmetic appearance otherwise that print was successful, nearly 15 hours and no issues.

 

Posted : 27/06/2019 2:07 pm
vintagepc
(@vintagepc)
RE: Thermal Runaway Error/Bed Preheat Error

Many people reporting these kinds of bed issues have found the heatbed connections to be either loose, melted, no power from the supply, or a blown heatbed fuse. I'd start there. 

Posted : 27/06/2019 3:39 pm
Robert Crane
(@robert-crane)
Eminent Member
Topic starter answered:
RE: Thermal Runaway Error/Bed Preheat Error

Thank you...I will investigate it a little further before contacting technical support or doing anything else. My guess is something to do with cables, something got caught or worn out over time from repeated movements and/or rubbing. Hopefully, it’s something not too difficult or expensive to fix. I would think that if it’s the bed it’s self, it would be covered under warranty. It could be a fuse too as you said, but those should and do last a long time...most of the time anyways.  Maybe it’s just the thermistor wire got pulled out of place from underneath the Kaplan tape. Would that be enough In it’s self to cause the heatbed not to heat up also obviously a thermistor is a regulator for such?

Posted : 27/06/2019 4:10 pm
Dave Avery
(@dave-avery)
Honorable Member
RE: Thermal Runaway Error/Bed Preheat Error

not the thermister as it indicated temp rise when you hit the bed with the heat gun. does the LED on the heat bed come on? you can measure the resistance of the bed both right where the wires are screwed to it and at the plug on  the EINSY. I'm betting on a loose wire

Posted : 27/06/2019 5:20 pm
Robert Crane
(@robert-crane)
Eminent Member
Topic starter answered:
RE: Thermal Runaway Error/Bed Preheat Error

I do not have a multimeter to do that with, but I will inspect all of the cables and connections when I get a chance. My guess too is that it’s a loose or broken wire, maybe something got overlooked after I repaired the printer and started using it the other night. Just another annoyance that’s keeping me from getting things done and may or may not cost me some money too. Oh well, it’s all about living and learning when it comes to 3d printing as one day, I may become a professional at repairing them because I am learning all about everything that can and does go wrong with them and. Ore than once already, because of my own mistakes :). Happy printing 🙂

Posted : 27/06/2019 5:34 pm
Robert Crane
(@robert-crane)
Eminent Member
Topic starter answered:
RE: Thermal Runaway Error/Bed Preheat Error

Update:  After leaving the printer at rest for the day while I was at work, I first inspected the heatbed cable for damage and couldn't see any other than it was curled between the printer and the enclosure wall on the left side, which may or may not have restricted it's movement during printing.  I then went into settings and set the temperature for the bed to 60 and it heated up fine and maintained that temperature for a few minutes (without the plate on the heatbed). I then moved the bed back and forth a few times and noticed some slight fluctuations in temperature of the heatbed, between 53 and 64 degrees.  I then raised the set temperature to 62 degrees and the heatbed again heated up to that temperature and maintained it for a few minutes, only fluctuating by one or two degrees at most.  I then proceeded to do a 2 hour test print (benchy) which is still in progress.  After more than 30 minutes, the heatbed has maintained it's 60 degree setting.  I didn't inspect the thermistor or anything else on the printer as of yet.  I suspect that there may or may not be a tiny connection issue with the heatbed cable it's self which at this point, may not even be likely.  I will inspect in more detail next week when I have time.  3D printers can be and are tempermental at times LOL.  Thanks everyone for the suggestions!!!!

Posted : 27/06/2019 10:19 pm
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