I connected it now to the aquaero 5 LT that I have. In the flow port. It also says 0.0 l/h.
I don't understand how this could happen? I mean OK I have it for 6 months but I would assume that It should last more

That thing ain't cheap too..
I will wait for some Shoggy answer. If there is anyone who knows what could be wrong its him.. I hope I don't have to RMA the thing because in the spot it is now I will have to dismantle a large part of my loop to get it out..