I have a Worcester Greenstar. This is my first time attempting to Back Fill as the Boiler is 18 mths old. I am able to insert the Key with the arrow to the left under the open lock symbol. I hear the key 'click' in but when I try to turn to the locked position/symbol the Key just keeps turning. I know this could indicate that the Key is not in fully but I really am unable to push it up further. I am worried about asking someone stronger to have a go incase the Key, or anything else snaps! nor do I relish the idea of paying for a Plumber to come out. Does the Key look to anyone as if it should go up more?Anyone else had this issue. I believe the warranty is only 12 months.