Reusing a combi boiler without hot water circuit connected?

Hi, this might seem like an odd question - currently I have a combi boiler providing my hot water. I am i the process of building an extension with multiple bathroom/showers, and on the assumption that the combi flow rate (11.5l/min) will not be man enough, had planned to install a pressurised hot water cylinder (Telford Tempest) to supply hot water. The builder has specified a new boiler of identical heat output to the existing combi, so I am wondering if it is possible to resuse the existing combi with the hot water circuit isolated, or with a minimal loop attached to a single nearby sink? In theory this looks possible but was wondering if anyone has done similar or knows of any reason why this shouldn't work?

Thanks, Mark.

You will be able to use the exsisting boiler and add a zone valve for the heating circuit, zone valve for the hot water circuit & you may want to control the new extension with a zone valve & thermostat.
(assuming the boiler is sized correctly)
You could use the DHW side of the combi boiler to feed utility & kitchen sink.

Was the boiler sized by the builder or a heating engineer? You need to ensure that this has been sized correctly & you can get a good idea of the required boiler size by using an online whole house calculator.
Unvented cylinder coils tend to demand alot of kw, some mfrs around 25kw, usually overcome by staggering the heating/hot water programmes.

Thanks for the reply gasman. The boiler required has been sized by a heating engineer. I should have mentioned that the new extension is part wet underfloor heating - assume this doesn't make any difference? What you suggest sounds very sensible and avoids me having to skip a perfectly good boiler.

Thanks, Mark