Have you tried a reset of the electronics on this?
If not then try that and let me know what happens.
Open the door, switch off by using the on/off button.
Switch on, don't wait for any lights, as soon as you press the on/off button, press the program button 4 times within 3 seconds.
This will illuminate the two end lights (may be flashing).
Press the program button once, the first light will go out.
Now switch off, wait 20 secs. Switch on and off again.
Ok no worries.
As there is no leak and you have already replaced the flood switch in the base then all it can be is a faulty control board or broken wire in the door loom.
What you need to do is remove the outer door panel and there you will see the wiring loom. Split it open and check for any broken wires. Look were it goes down the door to he underneath as that's usually were they break.
But if the wiring is fine then im afraid you are looking at a faulty control board thinking the switch is activated when it isn't. There isn't anything else it can be for this fault.
The control board is in the top of the door. Remove the plastic frame at the top of the door and you will see the control board in there.
But they are very expensive. You are looking at about £200 just for the part im afraid.