Weak flow on upper floors is almost always about head — the height water has to be lifted, plus what it loses on the way.
Common causes
Insufficient height difference. A roof tank that sits barely above the top floor generates very little pressure. Every metre of height gives roughly 0.1 bar.
Friction losses. Undersized pipe, long runs, many bends and partially closed valves all consume pressure before the water reaches the outlet.
Scale and debris. In hard-water areas, gradual build-up narrows the effective bore over time.
Simultaneous demand. Pressure that is adequate for one outlet collapses when several open together.
The fix
A booster pump raises pressure at the point it is needed. Where demand varies through the day, a smart pump with integrated speed control holds pressure steady instead of cycling on and off — more comfortable and easier on the equipment.
