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Single Pipe Central Heating - lockshield valves necessary?

Discussion in 'Plumbing and Central Heating' started by daverk, 24 Sep 2010.

  1. daverk


    13 Jan 2010
    Thanks Received:
    United Kingdom
    Earlier this year I had some questions about my CH (I moved to this property last year) which was not working on all rads. The original post was here http://www.diynot.com/forums/viewtopic.php?t=209351 and I had some helpful comments from stem.

    I'm just about to do the work. It is mixed 2 pipe (which is OK) and 1 pipe, and the part that will be upgraded is the 22mm Single Pipe which has 6 rads on it. The property is old and does not lend itself to converting the 1 pipe to 2 pipe easily, so I want to try getting the single pipe working better if I can. 4 out of 6 rads get reasonably hot (but could be hotter), and 2 of the 6 just get lukewarm at the tops.

    I have recently discovered that the main Single Pipe flow and return seem to have been reversed when the combi boiler was fitted some 8 years ago, which won't have helped matters, because the (standard 2 pipe type) TRVs (rad inflow) are now on the far end of each rad, and the lockshield valves (rad outflow) are all nearest the boiler. In addition they are all bottom entry, bottom exit.

    So the plan is:

    1. I have acquired some Danfoss RA-G15 Thermostatic valves which are large bore/full flow to put on the flow side of each rad, and they will be top entry into the rads.

    2. I am re-routing the main 22mm Single Pipe of the 2 cold rads where it is possible so that the rads sit directly above the main pipe, to optimise gravity circulation via their 15mm flow/returns.

    My question now is: are lockshield valves really needed at all on rads in a Single Pipe system?

    The lockshield valves already fitted (they are all fully open) are 15mm but the actual gap left in the valve for water to flow is very small. Presumably they are designed for pumped systems where a small gap doesn't matter so much. As I understand it, gravity-fed rads fed from a pumped Single Pipe system do not need to be balanced, and the lockshield valves should (generally) be fully open. (NB the 22mm Single Pipe seems to keep quite hot at the far end of the system).

    So it occurred to me - should I remove the lockshield valves altogether and instead fit 1/2" male x 15mm Comp into the rad returns, with an isolating/service valve below, to maximise flow out of each rad (because these fittings are less restrictive than a lockshield valve)?

    Any thoughts/experiences would be appreciated, and if fitting a service valve instead of a lockshield valve, which brands/types are resistant to temperature etc (my experience with quarter-turn service valves is that they seem to leak after a couple of years because the seals are poor, especially if they are actually turned off/on!)
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  3. John506


    14 Nov 2006
    Thanks Received:
    United Kingdom
    Considering your rads are warm and the top and cold at the bottom, they probably just need cleaning out.

    Lockshield on one side and a TRV on the other.

    You could put whatever big bore valve on a radiator, but then if u stick an iso valve on the flow, you will choke it to 12mm anyway.
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