I got it wrong, I had to drain the radiator and swap it around. :rolleyes:
It's interesting though, I have a very similar column radiator in the master bedroom but from a different manufacturer, that one didn't have flow/return marked, so I guess it didn't have a flow diverter installed. It...
I know this is an old thread, but I also just fit a new 2 column radiator without knowing which is flow / return. I'm about to find out today if my 50/50 chance of getting it correct has paid off.
I've replaced an old Type 22 double panel radiator in our living room with a nice 2 column oxford one, I managed to find one with matching centres so didn't have to mess with any pipework.
When I first filled it up and checked for leaks there was tiny bead of water right where the valve...