exact same thing, so what exactly are you trying to drain ???? you have fecked up somewhere, not recommended but you have fecked it anyway so just open your new PRV and use that as a drain, hopefully will seal after you have opened it
I'm just draining at the proper drain pint on the boiler mate, no **** ups, it's draining ALL the system above/upstairs though!!
Here's the PDF with drain point, Page 19 - https://www.ccha.org.uk/wp-content/uploads/2016/03/Ferroli-Optima_701_Manual.pdf
It's just a soldered T on the CH out. (see my pics above)