Determining flow/return pipes of radiator

[paulwf]

I removed a radiator several weeks ago, and I now wish to fit a towel rail with TRVs, however I don't know which pipe is the feed and which is the return.

Is there an easy way to work out which is the feed and which is the return? The system is currently drained down.

 

[chrishutt]

If the TRVs are bi-directional (most are) it doesn't matter which is flow and return, if you're making bottom opposite end connections. Also there's not much point in fitting TRVs on towel rails since the heat output is unlikely to be excessive, especially with towels insulating it.

 

[TicklyT]

The easiest way is with the system running - the flow warms up before the return.

If you have a bi-directional TRV (often marked with two opposing arrows for flow direction), it shouldn't really matter which pipe it's fitted on.
Can you trace the feeds from another rad. that already has a TRV fitted?

 

[paulwf]

The towel rail came with a TRV, but unfortunately it is a single directional one. But I should easily be able to see which pipe is connected to the next rooms TRV.
If not I guess I could just fit it, and then turn it round if its the wrong way.