"Doctor Evil" wrote in message
...

snip

He is wrong. Divide and rule. Try two combi's. one doing one shower,
one
doing the other. Combine the outlets for the baths to fill them
quickly,
using non-return valves and a shock arrestor on the bath side on the
non-return valves.

Have one combi do upstairs heating and one do downstairs. Simple and
cheap
and effective. Have each combi have its own gas supply right back
to the
gas meter.

Check the mains water pressure and flow. Replace the mains stop
cock with a
full-bore stop cock irrespective, and have dedicated 22mm cold
supplies to
the combi's from the stop cock. Take the cold supply for each
shower off
the combi supply just before the combi. Any pressure fluctuations
on that
line will be equal on both cold and hot at the shower.

Combi's are cheap.


But the work to install all of the above isn't.....