hello, i need to change the float valve for my cold water tank, as it not functioning correctly. the current valve is a part 1, am I right in thinking that I need to replace it with a part 2? I have seen versions marked high pressure and low pressure - I assume I need a high pressure one as it will be connected to the rising main? also, can anyone offer some general tips for doing this? are there any great differences in connecting a part 1 and a part 2? the old valve is covered in scale and verdigris, and so I think it's going to be tough to remove it. lastly, there is no way of isolating the tank without shutting off the water in the kitchen. Is it worthwhile adding an isolater for the tank? What would be the best choice? stop cock, ball valve, gate valve, etc?