vented hot water cylinder, can't undo top nut

[lazyade]

Well today I was trying to help a mate out in adding a surrey flange to a vented h/w cylinder, but we can't undo the existing fitting right at the top of the cylinder. Anyone have any tips? And anyone know what size spanner or socket is needed (I think they only way we're going to get it undone is with a socket or ring spanner on it), it looks like it's 35mm - but I might be wrong.

Thanks

 

[swbjackson]

How are you trying to do it? I normally leave the cylinder full of water for strength and just use a spanner on it. If it's really tough I get my 18" adjustable out. You may have to apply heat if it's really seized.