Radiator pipework

[Bullbags]

I need to replace an old rad with a new one. The existing one has two identical very old looking lockshield valves on either side. There is very limited pipework seen coming to the rad. I am fitting a TRV on one side but am not sure which is the flow and return. What is the best tip to tell which is which? I'm thinking turn the system on and see which pipe warms up first. Any other ideas?
Cheers

 

[Nixt]

I'm thinking turn the system on and see which pipe warms up first. Any other ideas?
Cheers

That usually does the trick. The other way is to buy a bi-directional TRV then it won't matter.

 

[Bahco]

Will not matter as the new TRV should be bi directional and can go on either end.

 

[lightning]

I need to replace an old rad with a new one. The existing one has two identical very old looking lockshield valves on either side. There is very limited pipework seen coming to the rad. I am fitting a TRV on one side but am not sure which is the flow and return. What is the best tip to tell which is which? I'm thinking turn the system on and see which pipe warms up first. Any other ideas?
Cheers

might have two lock sheild valves for a reason ,you haven't a room stat in the same room as the rad