hi can anyboby help ive just replaced my mixer shower in bathroom and when put new one in it only runs at very hot water and wont turn down to cold at all so then i took it back off and tryed it the other way round and then it would only worked that it was cold all the time and couldnt get hot water .the old one woked fine but we replaced it as had new bathroom .so just cant get the new one to mix at all any help would be great