"Cursitor Doom" wrote in message
...
On Fri, 08 May 2015 22:02:03 +0100, The Medway Handyman wrote:

Most TRVs are multi directional.

Unfortunately, this particular one isn't.

Assuming the whole system is drained down.

Turn off the circulating pump isolating valves.
Disconnect another radiator (as close as possible to mystery pipes.)
Close valves on all other radiators
Connect a garden hose to one of your mystery pipes.
Turn on water and see which pipe it comes out of on disconnected radiator.
It will be the same (flow or return) as the one the hose pipe is connected
to.