At the end of a 2+ day print I ran out of filament right at 99%. This happened while I was at work so the printer sat for several hours waiting for me to change filament. When I got home I put in a new spool, acknowledged the alerts on the screen, pressed resume and walked away for dinner. I only had about a dozen layers till completion but hadn’t gotten a print complete notification so I opened the app and saw the nozzle temp was 42° and the bed was at 121° with a target of 35°. I’m printing PLA, so I was a bit worried about the bed being so high. I tried manually setting the bet to 35° but it kept rising, next I tired to pause the print but there was no response, I tried to stop the print but still no response. I tried the same commands on the touch screen but nothing worked. I was afraid something would get damaged or worst case start a fire so I hit the power switch in the back. I let everything cool down before powering it back up. I haven’t tried another print yet but so far everything seem back to normal. Has this happened to anyone? I tried searching for thermal runaway but only noticed nozzle posts.
I have never heard of a BBL heatbed runaway. Were you able to check the temp with another temperature measuring device. Ie ir gun or thermal camera
Easy enough to lick your finger and touch the build plate. If it doesn’t sizzle, it’s not at 130ºC. 
I suspect a problem with the sensor, or the hardware that reads the sensor, or maybe a FW bug. It wasn’t that hot. Classic “power off/on to fix” situation.
No, but the bottom of the castle I was printing became a little deformed from pulling it off a hot bed. You could also smell the PLA.
That’s a good test. Idk if it really was 130° but it was definitely hotter than 35°. It was hot enough to deform the PLA. I hope you’re right with it just being a brain fart for the software. If it happens again I’ll do the sizzle test and update the post.
Please submit a support ticket and send in the logs so our Engineer team can see if 1) it really did happen, and 2) what might have gone wrong.
Yes it showed that on the screen so it very well might have been real and not just bad data on the printer. But when we see the logs we should be able to identify the problem. You are right to be concerned and this is the first one of these happening on the heat bed I have seen.