I don't know your particular machine, but I'll offer some general observations... The steam boiler is overfilling because the water level probe is failing to detect ground, so it doesn't turn off the pump. The probe could be covered with scale so it fails to detect ground, its connection could be loose, or the boiler water has so few minerals, it cannot conduct electricity (e.g., water treated with reverse osmosis).

Although Eric's photos/diagrams here are for the Quickmill Vetrano, they're close enough to aid the understanding of your machine's similar functionality.