About a year ago we began planning on changing the heating system, I
immediately came to this group for help.

At first the plan was to go for a standard 30kw combi boiler and just
live with the poor flow rates experienced when two taps are opened at
the same time.
Then I thought why live with difficulty if you dont have to?

So the plan changed and I planned on getting an unvented cylinder with
a system boiler, the plan stayed like this for months and I done lots
of research before actually calling an installer. The first installer
came along and measured the cold water flow rate, me being my stupid
self forgot about doing that. In turned out that the flow rate was
only 23lpm which wouldn't be sufficient for the unvented cylinder and
worst of all even if I got an unvented cylinder it would not fit in
the narrow airing cupboard!

So we decided on getting a vented cylinder with a system boiler
because we also wanted a radiator in the loft.

Then the next installer came and checked the cold water flow rate and
the hot water flow rate,
the hot water flow rate was only 7lpm. The installer said that if we
got an unvented cylinder it would still be better than what we got
despite the 23lpm flow rate. So we decided on getting a storage combi
(Vaillant ecoTEC plus 937) which gives 20lpm and when the store is
depleted 15lpm.

One installer said that if we channel the concrete floor for the
copper piping the copper piping will corrode and it will burst.
Is this true?

We also want the new boiler to run two different heating zones, is
this possible with a combi?
The Vaillant VRC 430 weather compensator can run more than one heating
zone so that's not a problem.

And finally the Vaillant weather compensator plugged into the boilers
control panel and requires no room thermostat (according to Vaillant)
so how does it know when the target temperature has been reached?

Thank you for all your co-operation, and special thanks to:
Andy Hall
Ed Sirret
Roger Mills
Owain
The natural Philosopher