From the DPS site:

"GX units are only suitable for a vented boiler / heating systems with
a Feed & Expansion Tank."

I've never seen a presurised heat bank advertised. You lose many of their
advantages by doing so. They would require much more expensive type
approval, too. Unpressurised heat banks can be used with pressurised central
heating systems with the use of additional heat exchangers and pumps (or
indirect coils). This is usually safer and more convenient.

Christian.