:Cool: In that case? Try turning the lock further around. My Dethleffs has a problem that you need to turn it in a certain way. 2 locks on the Gas locker both in different positions. Perhaps a photo of your lock may help us to sort it for you?
If its the usual type fitted to most brit and european motorhomes, the lock is only designed to turn 90 degrees.
Difficult to describe the process, but here goes:
You should be able to offer the cap onto the housing and it will turn about 90 degrees clockwise to locate on the housing, and stop. Insert the key and turn the key only 90degrees clockwise and withdraw. You should now be able to turn the cap clockwise without it coming off.
Note: turning the cap anticlockwise when locked often results in the cap coming off - the retaining lugs are soft plastic and will not stand up to any real force. The fact is that the 'lock' is more of a visual deterent than a physical one.
Some of the water caps are notoriously cheap and nasty - the one on our new Adria failed instantly, seems to be similar to the one you describe. We had a similar problem with an Autosleeper cap on our previous van. I got a new cap (eventually) from the dealer, and fitted the lock, which just slots into the middle and it seems ok now although the build quality doesn't excite......:Confused:
We had these type of water caps on our last van and I purchased a replacement and that also went faulty very quickly.
I stopped locking it as it took too long and was a little hit and miss.
They are total rubbish!
If you need to lock it, I would recommend that you find a different type.
Just my opinion