Hi TGF - apologies for reviving the thread - been looking on the forums and am active in a couple of related posts - did you sort out your issues? My set up sounds very similar indeed to yours - mains supplied the cold for taps/shower, PRV under sink to limit to 3bar, combination bloc has balanced cold not used. The cylinder is fed its water from a supply pipe from the mains which goes through the combination bloc and then into the cylinder. Do you have mixer showers/taps/monoblocs etc as most people probably do (with cold off mains directly and hot from cylinder)?
The manufacture date of my cylinder is January 2021. I have had BG/Dyno out a few times but with little success and the cylinder bangs (not always) when heating up - it appears to be worse when hot water is drawn down a bit. I have contacted Gledhill to see what is going on. Depending on what happens I may have to call BG out again. Regardless of when it was fitted, it was them who did so and I do have the Homecare cover so hopefully I can get this resolved somehow..