When you use the filling key on the Bosch Worcester, you might be a little bit shy and feeble, it's plug-&-play with a little bit of a push.  Don't over-do however and break the mechanism or key! But you have to insert it with a little bit of force *when the pins are aligned* it will go in.  You need the same amount of pull to get the key out.  The Bosch Worcester filling mechanism can take a little bit of push and pull, like opening a tight jar, you will not be using a hammer!
You will know when the key isn't in because you'll have water on your face.  This little tip will save you a £50 non emergency call-out charge I'm sure ;)
                
 Mr Plumber
                
 December 2007