Water pressure and flow

[Broadback]

Sorry for this, I know it has been discussed before, but I am unable to get my head around it. Water mains comes in to stopcock. It then goes to the outside and kitchen tap through 15mm copper. To get the water upstairs it goes through a 15mm plastic pipe, with the reinforcers (very small holes) up to the bathroom. Now it is back to 15mm copper to feed the toilet cistern, cold basin, cold bath and combi boiler. The flow from these taps is considerably less than downstairs. Is this simply due to the fact that it has to rise 10ft ish, or would it be better to replace the plastic 15mm with copper 15mm? TIA

[IMM]

If the pipe from the kitchen tap to upstairs is 10 foot or so, it shouldn't make much difference. Are the bathroom taps mains pressure? This can reduce flow if your mains flow is not that good. If not, then it appears that the plastic is to blame. This is a problem much overlooked with plastic piping. If you can get 22mm copper up there all the better. Also replace the main c*ck with a full bore. Try this first.

[Set Square]

The reduction in flow is more likely to be caused by the restriction of the pipe rather than by the 0.3bar drop in pressure due to the height difference.

Have you measured the flow at the kitchen tap and at the bath tap (calibrated bucket + stopwatch) to see how much difference there is?

15mm copper would be better than 15mm plastic since it has thinner walls and thus a larger bore. From an installtion point of view, it might be easier to use 22mm plastic which would achieve the same thing, or better.