Miele G646 sc + Inlet/Drain” indicator

Miele G646 sc + Pumps out no problem, but when it fills it fills for about 10 seconds water comes into the presure chamber on the side then the water stops and the “Inlet/Drain” indicator lights up then flashes alternately.

wait for another 10 seconds & it starts again and repeats this process.

I have checked all filters inlet and inside machi,e. removed the bottom tray so no obstruction from float switch.

I have checked all valves & the reed switch in the presure chamber. All Ok

The customer has changed there powder for the first time in six years could this cheap powder be blocking the presure chamber ??

Can anyone help?

Thanking you