When the system is idle the pressure is currently 1 bar and
when it's in demand it's nearly 2 bar.

That sounds like it is behaving precisely as designed. When filling or
checking the system, ensure it is cold. If it rises above 2 bar, then you
may have a problem, though. This would probably be an undersized or
malfunctioning expansion vessel.

BTW, this is totally unrelated to the fact you have an unvented hot water
cylinder. It is the pressurisation of the primary circuit which requires the
pressure gauges and filling loops. You can have this system on a gravity fed
hot water cylinder too. It sounds like it was converted at the same time as
the cylinder was installed, though.

Christian.