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Automatic bypass valve passing?

Discussion in 'Plumbing and Central Heating' started by MJN, 28 Dec 2020.

  1. MJN

    MJN

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    Our CH system has an automatic bypass valve fitted but it has always been closed off (or at least set on the max value of '7') as we have three radiators without TRVs hence it was assumed it is not needed.

    I discovered today, however, that the bypass valve appears to be passing. Specifically, measuring the pipe around 10" downstream of the bypass valve with an IR thermometer shows it pretty much tracking the flow temperature. I've always known this downstream pipe to be get warm/hot but put it down to it being a vertical tee'd into the return pipe to the boiler and hence just thought it was picking up heat from that (and perhaps conduction through the metal of the valve from the flow pipe). Only now that I've measured do I think it is actually down to hot water passing through it.

    [​IMG]

    Is this a known issue that can affect these valves? If so, is there any remedy other than replacement? If not, does anyone recognised what make it is (the marking appears to be be 'USV 16/22')? Alternatively, could I just remove it and cap either side off instead, noting that we do have a free path available through rads without TRVs and the bypass has always been closed anyway?
     
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  3. ianmcd

    ianmcd

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    that is the maximum setting, if you want to shut it off 1 or 0 if the valve has it
     
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  4. MJN

    MJN

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    Thanks for the quick reply Ian. Are you sure about what you've said though? Surely the higher numbers refer to a higher threshold for opening up? Certainly lowering the setting on this one appears to result in what sounds like a greater flow through it.

    Whilst I haven't found the instructions for this particular valve I *think* it might be a Pegler and the instructions for their USV22 appear to suggest the higher numbers correspond with higher thresholds for opening. This would certainly fit with my logical thinking of how these things working - 'tightening' the knob clockwise (towards the higher numbers) would compress what I assume to be a spring inside thus increasing the pressure required to open the valve.

    Edit: Now that I've been fiddling with it I appear to have a slight weep forming. Grrr. That'll teach me to mess with things in the middle of Christmas!
     
    Last edited: 28 Dec 2020
  5. Mottie

    Mottie

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    Im not a professional but the way I set mine was to wait until my system had cooled right down and turn off all my TRV's but leave the rads without TRV's on - in my case just the lounge and bathroom. I then fully closed off my bypass valve, turned my room stat up high and put the heating on. When closed, the bypass should remain cold. Let the rads get up to temperature and then start opening the bypass valve a bit at a time while feeling the temperature of the bypass. At one point the bypass will start to get hot when the valve starts to open. Close it off a quarter of a turn and that should be it. In future, the bypass should remain cold or slightly warm but when you turn the thermostat down or switch the heating off and the boiler is on the overrun, the bypass should get hot almost instantly. I do reset my bypass in summer when the heating is not used, just the hot water, when I change the pump speed.
     
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  6. MJN

    MJN

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    Thanks Mottie, but my issue isn't really how to correctly set the bypass value it is rather that it is passing even when on the highest setting despite there still being a free flowing path through the system. This short-circuit is raising the temperature of the return pipe and seemingly causing the boiler to prematurely cycle.

    What I suspect has happened is that there's either some debris on the valve seat, or the valve washer has otherwise perished and it is therefore failing to close when it should. I am inclined to remove it entirely on the assumption that I don't need it (my boiler doesn't require an overrun and I've got three rads without TRVs anyway) but I wanted to run it by you all here first for a second opinion as to whether this was a wise move or not.
     
  7. denso13

    denso13

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    Yes, it could be capped off easily enough.
     
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  9. MJN

    MJN

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    Great - thanks. What I might do is buy a couple of stop ends ready and then see if the valve can be dismantled first to check for anything obvious. If not then I'll whip it out. I say 'whip' but I'm sure it'll be anything but being in the confines of the airing cupboard and won't quite seal on first go knowing my luck. Speaking of which, I only refilled with inhibitor a week ago so not great timing for a drain down!
     
  10. Mottie

    Mottie

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    Might just be worth turning it in the other direction just to absolutely confirm that the higher numbers really do mean that it’s off. It doesn’t on mine. Will cost you nothing and take minutes. If indeed the lower numbers open the valve, it may even push any debris off of the seat and clear things up.
     
  11. MJN

    MJN

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    Sorry, yes, I had given it a go just in case my assumptions were wrong. It's a good idea about increasing the flow to clear it though - I recall doing similar with PRV that was once weeping.
     
  12. MJN

    MJN

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    I forgot to close this one off but thought it worthwhile for the sake of the archives...

    I removed the bypass valve and indeed found it be passing regardless what setting it was on. The spring was still intact but it seems that the valve seat wasn't sealing regardless. If I still have it I might dismantle it to see exactly why - I certainly didn't see anything stuck in it.

    Something which might be of use is that whilst Pegler sold this valve with the 'USV 16/22' marking they no longer do. However, Siemens still do and whilst it is identical and carries the exact same markings on the valve they actually market it under the 'BPV22' product code:

    [​IMG]

    Widely available for a variety of prices (upto £60!) but I picked a new one up off ebay for a tenner.

    Having now replaced the valve the boiler has stopped short cycling.
     
  13. Mottie

    Mottie

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    What numbers are minimum and maximum flow on that one?
     
  14. MJN

    MJN

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    0 is lowest (easiest to pass), clockwise to 7 is highest (hardest; effectively closed as tight as can be noting it's a spring so could still open given enough pressure).
     
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