It's not a pressure reducing valve but a automatic filling valve, they look similar so I can understand the confusion. your installer was correct, he fitted a filling loop, you must turn it on to pressurise system and then off, it does not automatically fill you system when there is a drop in pressure.
I wouldn't fit an automatic filling valve, it would always be a fillling loop.
I wouldn't fit an automatic filling valve, it would always be a fillling loop.