Unvented pressurised system - some say you can’t add a shower pump - technically why (forgetting any legal restrictions if there any)

[Elkato531]

Clearly none of the problems being touted are real

Well you clearly know best. Obviously the water regs are there to restrict your freedom to do what the hell you like and not to help ensure adequate supply and water quality for everyone.
If you are looking for validation for breaking the rules, you're in the wrong place.

 

[Mikerightsecondtime]

Well you clearly know best. Obviously the water regs are there to restrict your freedom to do what the hell you like and not to help ensure adequate supply and water quality for everyone.
If you are looking for validation for breaking the rules, you're in the wrong place.

So you are saying it is impossible to boost pressure at a 2nd floor shower, if the shower runs on an unvented system. Is that right? One way would be to put a pump on the shower feed, but you think that’ll be like Chernobyl, so what do you suggest - or is it just ‘computer says no’ and we can’t look beyond the obvious or what the rules say

 

[Elkato531]

As already mentioned, if you have 3 bar incoming pressure you should still have 2.3 bar at a height of 7m. There will be a little extra pressure loss due to resistance of pipes and fittings but there will still be more than enough pressure for a good shower. If you have poor flow, the problem will lie with the flow rate and not with the pressure. Flow rate is mainly affected by restrictive pipes (usually the pipe from the external stopcock into the house) and this is where you can make the biggest improvement. Many properties have 1/2" copper pipe and older properties may still have steel or lead pipe. Internal corrosion, particularly of steel pipe) can reduce the internal diameter significantly. Upgrading to 25mm MDPE can make a large improvement.
Your installer should have tested both pressure AND flow rate before advising on an unvented system. Unfortunately, many installers fail to do this.
Attempting to boost the pressure to deliver more flow would be a bodge tackling the symptoms and not the causes. And, as you already know even if you fail to understand the reasons, it would be against regulations.