Thanks a lot for taking the time to reply!
Yep - pressure dropping (this morning to 0.6, usually to around 0.7-0.8).
Also fluctuate between hot and cold (2.5 when hot after a run, then drops to around 1.0 when cold), which made me think that it could be the expansion vessel.
I assume...
Had one of the above fitted 5 years ago or so.
Last year it started to show signs of loss of pressure in the expansion vessel, so had it pressurize back to normal.
Over the last few days the boiler started to leak very badly - water coming from somewhere on the right hand side if you stand...