In message . com, nazn
writes
Thank you John for the information you have provided, I have looked up
the part and am seriously considering this option, however before I go
down this road, I would like to attempt to let air in one of the
radiators, as a temporary solution. Any idea's how one would go
around doing this?

Drain down the system a bit, letting air into the rad. Refill but don't
bleed one rad (or not fully anyway).

As for the expansion vessel install would I need to isolate the
existing unit? If this is the case this sounds tricky

Don't imagine so.
--
Chris French