Thanks Christian for the fast response.
Yes I did notice yesterday the pressure had dropped, I topped it up and
I see it has gone down again, and I have just looked outside and there
is a slow drip from the pressure relief valve pipe. Hopefully it just
hasn't seated properly, but it's an easy fix unlike the expansion tank.
I topped back up to 1.5bar and ran the hot water it creeps up to 2.4bar
and seems to hold there.
The hot water gets warmer but not as hot as it should be and not as hot
as the central heating radiators, it seems the diverter valve is still
not diverting most of the water? Shouldn't the system operate normally
while the pressure has been topped back up to 1.5bar ? could there be
another problem

Thanks
Dave