"Christian McArdle" wrote in
:

I'm a bit concerned about the gate valve on the return pipe - if I
read it right, ISTM it's a bit dodgy to be able to close off the
whole circulation like that

It is traditional to include a gate valve in order to balance the
system.

Thanks for explaining, Christian -as my post indicates I thought it was
directly in the return to the tank, after the HW and CH had been tee'd.
Struck me as very iffy!

mike