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