I also have a 30cxi, installed Jan 2005. In Aug 2005 the water inlet valve was replaced after a fault was found causing it to 'stick' in the closed position - so I could not re-pressurise after a loss (bleeding rads etc.)
The valve was again replaced in Jan 2006 for same reason.
A design mod. on the water inlet valve (by Glow Worm) necessitated a further change in Mar 06 and thereafter I had difficulty re-pressuring above 0.7 bar.
The boiler is designed to stop operating should pressure drop to 0.6 bar or lower, and when very cold, at night, this pressure can fall that low.
I have now had an external water filling loop installed and can pressurise to 1.0 bar cold. The natural expansion when hot causes op. pressure to be about 1.6 bar.

I'm of the opinion that the new, replacement water inlet valve assembly, having two non-return valves and an airbreak is having a reducing effect upon the pressure.

Finally, after much "debate" Glow Worm have covered the installation costs of the external filling loop and the original installer has today installed said item.

Note, it is rumoured that water supply companies are reducing their mains water pressure to reduce leakage from mains pipes. This could, with the internal filling loop resistance cause a drop in the water pressure available when pressuring from cold. That said, United Utils tested pressure at ground floor level at 2.2 bar, and as boiler is 3 metres higher one would expect 0.3 bar pressure loss. So, 1.9 available should pressureise the 30cxi to 1.5-1.6 allowing for a nominal amount of resistance resulting from the internal filling loop and now, with the external, there should be 1.9 available to it.

Still only able to pressurise to 1.0 bar cold though.