Hi,
it seems the whole issue has been caused by a large jar which blocked the tab-lid. Unfortunately the jar has a size which is just high enough to block the lid. Thus I wasn't able to spot this issue initially. Further I was to lazy to empty the dishwasher and doing the dishes by hand (lazy engineer
). Thus I tried the same unvaforable constellation about 5 times.
I would highly recommend to make a test run with an empty dishwasher, if anyone has similar problems in future.
Regarding the thermoactuator, it seems they are also called wax-motors. A websearch for wax-motor delivers more search results e.g. [1].
Here are also pictures of the actuator's piston and lever position, which might be of use for someon in future...