Is this thermal runaway?

I have a standard Creality Ender 3, probably bought it new in 2019 well before V2. I ordered a V2 a few weeks ago which had a defective board in the sense that the micro SD card wouldn't latch. Amazon sent me a new one board. Installed it, works fine. I took the bad one and put it in my old Ender 3 thinking I would rig something to hold the card in place. That works except for one thing-- the bed gets hotter'n hell. I usually run 60c and the gcode of my test program reflects that. But as I watch the display, it hits 80c pretty quickly so I shut it down. There seem to be settings for the machine itself which I also set at 60c. The heater ignored that as well as the gcode heat setting. Any ideas? I appreciate any help.

could simply be bad pid tuning.

The bed, heater and thermistors will be different in the two printers, so you probably need to do some pid tuning.

thermal runaway is what i had last week.
Tip for you. Don't start heating thr hot end with pid tuning turned on, and then disable it while still running the heater.
The billowing clouds of white smoke that were vapourised pla - was my first clue I'd done something stupid :-)
Proper thermal runaway is usually indicated by smoke.

badly tuned pid or just the wrong settings is characterised by large temperature swings.
So you might have found that the bed temp hit 85c and then went back down to 40 and then back to 85 and so on.

In your case - probably just needs pid tuning for the new setup.
Did you flash the new board witht he old machine's firmware ?
If not that might be worth a try as it'll put the old pid setting back.

It might bugger other things up.
I have no idea, but - no it's not necessarily - or even likely to be - thermal runaway.

"Did you flash the new board with he old machine's firmware ?"
I had a feeling someone might ask that. I don't know how to do that. If you are willing to break it down for me, I'd appreciate it. Otherwise I'll try to find out on YouTube. Thanks for the tip.