Miele Premier dishwasher G660 will not fill with water?

Hi,
I have a 2nd hand dishwasher.
I've cleaned the machine according to the operating manual; filled it with salt and rinse aid; matched the salt level with local water hardness and tried it; checked the hoses; checked the inlet filter and supply. Inevitably, there are some problems:-
1. Mostly (but not always) the machine fails to fill up. It completes the cycle including drying) but there is no evidence of any water being involved (An upright cup left in the machine remains empty)
2. The detergent compartment mostly fails to open. I've checked the solenoid and it works just fine. It may be linked to failure to fill with water.

Looking through various posts it seems this might be a sticking float valve but I cannot find out how to access the float value. There is a raised section in the middle of the floor of the washer which looks to be the right height to have water trickle in and trip a float to stop the machine over-filling. However, I cannot see how to get the top off check and if necessary free up the float.

Thanks for any advice on float valve access or any other possible cause of the 'failure to fill' problem