For what you gain it is not. Putting a new boiler on an old systems adds
little value.

You're now just arguing that the extra capital cost is justified. This is
very different from your original assertion that the capital cost was less.

Yes. You have to wait much longer,
as you have to wait for the combi to fire
up and get up to speed, unless you have
one with built in storage.

Are you having a laugh? You have to wait for the cold lag to empty in
adraw-off in a storage system.

Not only does a combi also have this cold lag (in addition to burner and
primary circuit lag), but the much reduced flow rate means that the cold lag
is of much greater time duration.

The wiring is NOT simple, especially to the uninitiated. The valves
tale up space and are another thing to go wrong which is expense.

If you can't wire up a zone valve, you are not a competent person to do any
electrics at all. It is less complicated than wiring a lighting point.

You still haven't a clue. Tankless on-demand (instantaneous, multi-point
in
the UK), is increasing market share in the USA.

Whilst there is no doubt that it is increasing market share, it does not
represent the installed base. I have no figures, but would guess that
instantaneous water heating of mains water is more common in the UK than the
US. It is not fair to compare the latest products in the US with UK products
that were installed 20 years ago.

Christian.