A8’s mainboard provides no strong MOSFET for controlling the heat-bed and the nozzle. Both components draw easily 15 A through the mainboard and the bed is limited to around 50°. It is important to get these 15 A away from the mainboard, otherwise it will surely burn down some day.
I got those 30 A MOSFET from Amazon for 13 € each. Directly connect the bed and the nozzle to the MOSFET and connect directly to power supply. The mainboard connector for the bed an nozzle become low current control outputs.
The green LED indicates that the MOSFET is powering the bed or nozzle. With this setup you can run the printer for hours/days :-)