Heating flow and return

[bighig1951]

I removed my bathroom radiator ages ago, leaving pipes and identical valves in place, but without noting which was flow and return. Having re-fitted the bathroom, I now want to install a replacement radiator. With most rads in my house I could feel the temperature difference on flow and return pipes but the bathroom pipes are at the end of a run and I can't tell the difference. Is there a dodge for this that doesn't involve holes in floors or ceilings?

 

[HERTS P&D]

Fit the radiator and then turn some of the other rads off and you will soon see which pipes are the flow and return.

Andy

 

[bighig1951]

Thanks, Andy. If I was simply leaving the existing pipes & valves in place it wouldn't matter too much. However, I'm fitting a bigger fancy column rad and a TRV. 1st - I've presumed a TRV needs to be on the flow end - now I've seen replies to similar topics which suggest TRV could be on either flow or return. 2nd - the rad instructions strongly recommend that air vent is at the return end.
This rad has a fixed blank so if I fit it wrongly I'll have to drain down to correct. I'm a bit of a novice + it's too darn cold to be without heating for long. Any help gratefully received.

 

[warmadmax]

depends on the TRV tbh, if its bi-directional flow, then it can operate either way

 

[bighig1951]

I think I've got it sorted. There is one rad beyond the tee's that I am looking at. Turned off pump to let pipes get cold, then opened that rad and turned on the pump just long enough to fill the flow side with hot but leaving the return side cold. Then drained some water from each of the valves where my b/room rad used to be. Much hotter water from one side. I'll try to connect tomo and hope I've got it right. This would probably only work when there is something beyond or very close to the affected pipework. Thanks for your input.