Thanks to @Krzysztof for the idea of using the nozzle as probe.
Because the thin steel sheet on the buildplate gets deformed due to the heat, the surface to print on changes a bit after every print. So it's needed to probe the buildplate, but unfortunately doing so is not so easy. The buildplate and printhead are always connected through the 50mm2 cable, so using them as simple swich would not work, but even if it had worked the controller board had needed a protection against the AC voltage. So I tried using a current sensing switch, which triggers the
Z Min Endstop when the current rises due to the nozzle touching the bed.
It works for homing and probing. I likely have to decrease probing speed or increase intensity to prevent the nozzle from pushing the buildplate down a bit.