On Sun, 10 May 2015 11:46:19 +0100, Jim GM4DHJ ... wrote:

wummin' just turn all the TRV's up anyway so they are a waste of time
.....

Yeah, thin-blooded creatures they are.

Some of the replies have given me an idea I'd like to put before the
Panel here. Suppose I connect a hosepipe to one of the two pipes using a
Jubilee clip and stuff the other end of the hose down the loo. Turn the
heating on. I then turn on the test pipe's isolator valve and wait one
minute at least with the water flowing down the loo. If after this time
has elapsed, the hose has become warm, I know that's the supply side. If
not, it's the return side. Does that make sense? Anything I've overlooked
here?