Welcome to the SeeMeCNC Community

Yes, I did dial it down to 20V and at first everything worked like a charm. It heated to 100°C in about 5 minutes.
But suddenly the bed only used about 7A for heating and couldn't hold the temperature.
I then took everything apart and measured the resistance of the bed: 2.7 Ohm

When I assembled everything and tried to heat it, the temperature didn't rise, so i touched it and found out that around 10cm in the middle the bed stays cold and on the outside it heats normal...

so looks like that I need a new one

Yeah, sounds like it died. You subtracted the test lead resistance when you did your measurement? I'm pretty sure SeeMeCNC does not recommend running the bed at 24V, so we're on our own here.

yes, i measured directly on the pads of the onyx.

but thanks. ordered a new one, that should arrive in a few weeks...