No need to change the valve if the machine is letting water in.
You've probably got a water softener in your house.
Use less detergent, & if possible, connect the machine to a hard water supply.
If the fault light for ' Drain ' & ' Excess Detergent ' come on frequently, then you probably have blocked inner pipes which can cause an air lock.
Call a Miele engineer.
Bernii
November 2010