Does a TRV need to be the exact size of the radiator inlet valve?

Discussion in 'Plumbers' Talk' started by j0hn, Nov 21, 2020.

  1. j0hn

    j0hn New Member

    I have a few of these old twin inlet valves I'm looking to get replaced but I'm not sure if a standard 15mm x 1/2" TRV and lockshield like this would work. I know the pipes are microbore and I think they're 8mm. I know that you can get an 8mm/15mm reducer that will allow you to use the 8mm pipe with the 15mm TRV linked, but not sure if there is something similar for the TRV when fitting to the radiator inlet. I thought all radiators have a standard inlet valve size but these look a bit suspicious, any way to know what size I would need without having to take it apart?

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  2. Mike83

    Mike83 Screwfix Select

    Search for” 8mm trv and lockshield.”
     
  3. j0hn

    j0hn New Member

    Is the "8mm" in reference to the pipe or the size of the radiator inlet? Also, how can I be sure the radiator inlet is actually 8mm without taking it apart. I tried some old school D = C/π by measuring around the valve but not sure how accurate this would be.
     
  4. Mike83

    Mike83 Screwfix Select

    The pipe inlet is standard 8mm.
    The thread on the radiator will be 1/2”
     
  5. j0hn

    j0hn New Member

    Ahhh! I think that makes sense, so confusing with the mix of metric and imperial. So thread size, whether it's 1/2" or 3/4" is about the radiator inlet. From what I've read online, 3/4" can be found in old radiators right? Just wondering if this radiator could be that old to be 3/4" because that twin inlet type is pretty old.

    With pipe sizing, would I be better getting 15mm and using a reducer for the 8mm pipe if in the future I get the pipes reinstalled again? I'm not sure if 8mm is the standard installation size anymore, assuming it's 15mm since all the valves are that size?
     
  6. Mike83

    Mike83 Screwfix Select

    Some trv packs that are 8mm are infact 15mm but simply include the reducer.
     
  7. j0hn

    j0hn New Member

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