PRV Installed on to Cold Pipe not Reducing Pressure Drainage and wastage systems and plumbing help, advice and answers

[ks9]

Hi There,
I have installed a PRV on the cold pipe to reduce the pressure for the shower mixer. But the PRV has not reduced the pressure. This is the second PRV I've tried. I have a high mains pressure over 5bar coming into the house. Any ideas or help please?
Regards
Kj