It should have an arrow on the body indicating the recommended direction of
flow.
Modern good quality TRVs such as Danfoss, Pegler, Honeywell etc are
bi-directional and quiet.
If yours is a cheaper make then it may not be bi-directional or quiet.

Davy

wrote in message
...
I recently replaced one of my radiators and took the opportunity to
fit a TRV. (There are none fitted to any of the other radiators).

Now the radiator (or just the valve?) makes a loud noise when the
system is running - not quite a hissing noise - more like a "rushing
of water" type noise.

If I turn the TRV up or down a notch, the noise stops for 5 minutes.
then starts again.

Any idea what could be wrong?

Thanks,
Mark.