Mieles do not have a seperate motor control board. They usually have a UI bord that controlls the cycles and UI and a second bord with all the "acting" parts of the electronics.
It actually sounds like a loose connection on the water level sensing system. Or the pressure tube not being connected. How long does it fill until it gives an error?
If the pressure sensor might be damaged, you may have luck or not. I don't know how this model is set up, but some Mieles have the pressure sensor built in on the second control bord. (This actually made a lot of less informed people trash their washer over here as they checked the pressure tube for blockages or the sensor for correct acting by blowing into the tube from the drum connection side into the sensor which mostly destroyed the delicate membrane in it.) If this somehow got damaged, you'll probably pay north of 150$ for the part alone (and usually 300-400$ total).
If it is one of the not so elaborate machines the new sensor will cost anywhere from 40-90$.
But honestly, probably just a messed up connection.
