Heatbed wont settle temperatur

Hi folks,

for troubleshooting reasons my setup first.
Cetus MK3 standart version, bought 2020.
Added Cetus heatbed last week.
External 24V 10A Powersupply. Voltage between the +24V and 0V terminal ~ +24.19V

When i choose an custom filament file, in my case PLA, the heatbed wont settle at the correct temperatur. I choose 50°C for the heatbed. When i preheat the bed it goes to 50 and holds it.
But when i start the print, with or without preheating, the teperature rises to 70°C.
Also in the top bar of Up Studio the measured temperatur in percent relative to the set temperatur
is displayed. And both are at 100% percent. The shown filament profile ist my costum own.
I would guess that something wasnt send to the printer?

Any suggestions?

greets Forgnod