Missed that ... only saw the comment about adding a PRV into the HW outlet therefore, I presume, to release any excess pressure and keep it to a 3bar constant? Perhaps I misinterpreted. That wouldn't be how this issue would be corrected though.
Are Gledhill's more liable to have this issue, can't say I've seen a recurring pattern specifically with them, rather more so the EV's. That's not to say there isn't of course but I haven't really seen it. In fact I recently had to sort the same issue with a Telford and then an Albion. Both had the tell tale showing @ the tundish. One needed a new EV the other just needed re-pressurised and tuned. I do carry a gauge to test the PRV is holding @ spec as the springs do get tired too, that and sometimes leave it connected overnight to check the fully heated static pressure, that can allow a closer set pre-charge in the EV. What is a constant though is poor or no servicing, every one I have gone to hasn't been looked at in an age. The other one I've seen is the HW stat has been played with so the HW temp has been altered which can have a bearing on pressure. One other constant though is age, I do believe that EV membranes lose performance the older they get and that may be a contributing factor.
