Coffee maker is clean and not plugged up and tank is full. Have to open pull it out many times or jiggel to get it to stop saying fill water tank. takes sometimes 10 minutes to get it to stop

SOURCE: I get the message Fill

The float switch is a proximity sensor. There's a float in the tank that triggers the notification when it leaves the proximity of the sensor, located on the right side of the tank cavity. Try cleaning everything and make sure the float is moving freely in the tank.

SOURCE: i have a miele coffee maker and it says

make sure there is no calcim built up in the water pipes ofyour machine. soewhere along the lines it gets a wrong reading.
you can run a few cups of vinegar in your coffee machine instead of water, then run a couple of cups of water to get rid of the smell of vinegar.
hope this works

SOURCE: The machine will say Fill water tank. So, we will

After filling the water tank, can you see if a grey plastic piece, in the back of the water tank, is floating?. If no, then that part needs to be replaced. If it does float, then the integrity of the water sensor, (located in the back of where the water tank is housed into), will need to be tested. Testing this sensor requires, tricking the coffee maker... that the door is closed. With Coffee Maker in the "ON" position, you will need to hold door switch in (located top right corner of unit, with door opened). As switched is held in, you will need to use a magnet and place it around the rear of where the water tank is housed into (Rear-left middle height area)... just around where the water tank float would be, if it were filled with water and inserted into the coffee maker. This sensor isn't visible, but is activated when a magnet is placed around it. If "FILL WATERTANK" message goes away, then replace plastic float or water tank itself.

SOURCE: My Miele 615 Coffee System

The water tank has a black float that runs inside a "tunel" in the watertank, and that is somehow conected to the water level sensor; if you are holding the tank and looking down into it, look at the corners to find the little tunel in which this black float runs.
In my unit, this "float" gets stuck down low sometimes (I have very hard sandy water) and I get the same problem, especially during descale. It is usually fixed by opening up the tunel (it has a small tab lid) and cleaning really well with a soft brush. hope this helps!