Our hot water cylinder has developed a pin-hole leak in the area around
one of the coil connections from the boiler. I plan to replace this
tank, and wondered whether the spacing between the coil connectors is
standardised?

It's very well fitted within an airing cupboard, and whilst modifying
the vent/water outlet and inlet pipes shouldn't be too difficult, the
side with the coil connections are more complicated, with little space
between the side of the cupboard, and plenty of existing pipework. It
would be wonderful to just put a new tank in and find that the pipes
line up perfectly...

Are there any issues I should expect when doing this? What sort of time
should I expect this job to take? I'm hoping to get it done on
Saturday, with possibility of Sunday or Monday if it all goes pearshaped
and lots of pipework changes are required.

I roughly measured the tank (tape measure straight cross the front,
top/bottom and left/right) and wrote down 45cm wide x 90cm tall. This
is including the insulation. Looking on line 400mm x 900mm and 450mm x
900mm appears common. Am I right in saying that tanks are measured by
their pre-insulated sizes? Would different width tanks change the coil
connection spacing? What about height? I was wondering about going for
a slightly taller cylinder as there's space...

Any advice is appreciated,

Thanks

David