Your diagram is too small to read but too big to study for free.
I'd guess floors 1 and 2 get hot water, 18 and 19 don't. You probably need balancing/regulating valves on the return branches, to reduce flow to the outlets nearest the circulating pumps and so increase the flow to outlets furthest from the pumps.
The flow rates should be very small, just enough to compensate for the heat lost from the pipes. The pipes are, inevitably, oversized for the flow rates. Similarly, the pipes have to be properly insulated. You need regulating valves on the return branches, sized to regulate the very low flow rates, to throttle down the excessive flow rates on the lower floors.
I have seen unregulated systems where the upper floors got no hot water and the return pipes on the lower floors (2"+ copper) were eroded at the bends due to the high flow rates.
Have a look at the Danfoss, MTCV valves, self-regulating thermostatic valves for hot water supply systems. They restrict the flow as the return water gets hot, making more flow available for where it is needed.
http://www.danfoss.com/United_Kingd...TCV/e340b0cb-566a-4e71-8a0b-9733a407123b.html
If there are dead-legs, or the water is only warm, there is a genuine risk of legionella. In the UK that could get you sued for huge amounts by irate guests; you might mention that if the management can't find money for improvements.