Many thanks for your thoughts on the reliability issue. It looks as
though Vaillant are probably the best bet at the moment. I take it
that this does not take initial cost into consideration? In other
words I am prepared to pay (a bit) more for a reliable boiler and
controls.

Having a 20(?) year old Baxi Boston 70 that has provided years of
service without any problems whatsoever, and listened to others
complaints about their new boilers, reliability of replacement kit is
a concern. As we are having a new bathroom which will involve
moving/changing the existing dhw cylinder I think that now is the time
to bite the bullet and look at a more efficient system.

More questions will follow!

rbel