One more question, do motorized valves produce a full shut off, such that
if
I use a motorized zone valve on the flow and a ball valve on the return I
can isolate a section of the CH circuit?

I wouldn't rely on it. However, the brand I used appeared to be as good as a
gate valve in shutoff, when I blew down one end. I would definitely fit
specific isolating valves if I needed such isolation, though.

Christian.