Back to my problem......

I've uploaded a diagram of the boiler plumbing see what you think..

http://www.ultimatereef.net/photopos...t=500& page=1


When I was tracing the pipework I was drawn to a connection on the
22mm CH pipework, I've always thought that it was just a joint but on
furthur investigation it appears to be a valve, it took a torch and a
hand mirror to view the arrow and " TOP" markings at the very back of
the valve, Now maybe this is the problem of the reduced flow to the
upstairs rads. The very front of the valve as a small screw in it,
which is as tight as I can get it but there is still a very small drip
of water coming from it.. I feel a little stupid in not reconising the
valve, as I said thought it was just joining two pipes together and
that the screw was perhaps an earthing point..Does the screw have any
function

Is ther a way to test if the valve is faulty??

Ofcourse it could be a red herring,

... Tony