low pressure in unvented system

[mcerbm]

Sheff Paul, It is 22mm into the flat, couldn't comment on what size is being supplied at the ground floor.

 

[PlumbBobBob]

you are always going to get lower pressure on the fourth floor than at ground level because for each meter in height the pressure will fall by 0.1bar. there is probably about 3-4 meters for every floor so would be 12-16 meters to the fourth floor which would be a drop of 1.2-1.6bar over the pressure at ground level.