I am trying to take the top off this tap so I can clean it out and change the washer. But it is stuck solid. On the cold one, you just unscrew the top bit in the middle that has the hot/cold symbol on it, then the top part which you normally turn for the water, just pulls off. But on the hot tap it will not pull off no matter what I try, can't move it at all. Any advice appreciated please before I have a disaster. Thanks.