"Egremont" wrote in message
...

From experience with an even bigger system it will manage normal
operation
fine

You mean with 4G F&E tank, and you find it doesn't overflow when heated
from
cold?.

Yes - though the ballcock is set almost to the bottom and the overflow is mm
from the top - hence the boiling problem. I would have liked to use a
larger tank but the roof-shape prohibits it. If it had been a problem I was
going to put another tank in parallel.