Havea Miele dishwasher that washers properly but no longer drys dishes
EDIT::::::: below info only applies if your water is not heating up … other than that you would want to start with a good cleaning and make sure you have rinseaid.
2 quick things to do: google “how to test dishwasher heating element” that is the metal ring in the bottom of the dishwasher it heats /maintains the water temperature and drying cycles…
this is a simple test with a multimeter. u must expose the side of the washer where the heating element exits the tub.
disconnect the 2 wires and set your multimeter to 200ohms.. so long as you get a reading between 1-50 the elemnt should be fine. if it shows damage u may want to replace it anyway.
next step is the thermostat (thermofuse?) this is a quick 20$ part that pops out with one screw. again google this there are a ton of youtube videos.
if that doesnt fix it then your in same spot as me. 
not knowing what to check next.
I should have been more descriptive. When opening the door after the dishwasher has run it’s cycle, I find hot air and a lot steam. I assume the dishwasher has a fan to remove the steam that is not functioning and causing the disks to not have been dried. Could this be the motor or fan assembly? Any way to test this?
I couldnt say. I believe that mine has an activated vent that opens when told to by the control.
I know that while researching my issue i found a video where a guy was talking about his activated vent and that it could stick open / closed..
possibly in your case, closed not venting the steam and allowing proper drying.??
but i am far from an expert. just a guy trying to fix his own dishwasher 