Okay cool but say i was replacing a rad and the two valves how would i determine which was the flow and the return. Obvious answer i guess is see which one heats up first.
Was just wondering if flow/ return had to go into TRV.
Thanks for the info
If you're fitting a TRV, one of them will have to go to the TRV. Not all rads need a TRV, usually the rad(s) in the room where the stat is shouldn't have one.
Most TRVs are bi-directional. Some like the Danfoss RAS range have a grey collar on them under the head that you turn to set it as flow or return.
Yes, the only reliable way to tell the flow and return apart is to see which one heats first. Unless you can trace the pipes back.
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