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A little confused about turning the hot water off..

Discussion in 'Plumbing and Central Heating' started by pavsid, 29 Jan 2015.

  1. pavsid

    pavsid

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    Hi all, i've been doing a bit of DIY plumbing, mainly fitting a new bath and sinks.

    The first time I turned the water off, hot & cold, I turned off the mains, then turned off the gate valve supplying the hot water cylinder from the cold water tank. I ran the cold water for a bit and it stopped very soon, as expected. I actually ran a bath with the hot water, and I understood this was normal as it was emptying the hot water cylinder. But when the pressure died down there was always a little bit of hot water trickling out the taps, and if I closed the taps then the pressure would build up until I opened the hot tap again and quite soon it would return to a trickle.

    Now i've turned all the water back on again, and everything is working fine. But since then i've had to turn the water off again to do some other work. So i've repeated the above - turn off mains, turn off gate valve supplying cylinder - but this time, and every other time since, when I run the hot water tap to drain the cylinder, it only runs for a few seconds before returning to that constant little bit trickling out - as though the cylinder doesn't have any water in it.

    So, two questions really:

    1) Why is the cylinder not draining anymore?
    2) Why is there a constant trickling, and how do I stop it completely?

    Been losing a bit of sleep over this one!

    Thanks in advance!
     
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  3. Burnerman

    Burnerman

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    Trust ye not ye olde gate valve......frequently they don't shut off fully, and actually belong in the days of steam :p
    It's not the copper cylinder that's draining.....that remains full. It's the supply from the loft tank that ceases the flow when that empties.
    John :)
     
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  4. gasmanstu72

    gasmanstu72

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    Yeah,
    Sounds like the gate calve is letting by, if the dribble isn't that much and you can manage it with some old towels etc. you could try cutting a new one in underneath the old one,

    If not, you'll have to drain the storage tank in the loft and do it.

    Oh, and make sure that you cut it in above the top level of the cylinder or you could end up getting wet! ;)

    Like the above poster says, the cylinder doesn't drain, the water flowing into the bottom of it stops, so it's still full of water right up to the top.
     
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  5. pavsid

    pavsid

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    Great, thanks guys, thought I might have broken something :)
     
  6. pavsid

    pavsid

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    Actually one other question - what's the best valve to get to replace the old one with? I need to drain the cold water tank anyway to fit another outlet, so may as well replace that valve at the same time.
     
  7. gasmanstu72

    gasmanstu72

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    another gate valve I would say,
    gate valves give you full flow through it, stopcocks and the like are too restrictive.

    providing its open fully, there's no harm in leaving the old one in if its in an awkward spot, , just take the handle off it and fit a new one in where you can
     
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  8. pavsid

    pavsid

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    Ok, cool, i'll get another one of those. Thanks.

    I think i'd struggle getting another one in above the cylinder, so may as well replace the old one complete. Will save me cutting more pipes as well!
     
  9. pavsid

    pavsid

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    Sorry, one other question!

    How do I drain the cylinder? I need to fit an essex flange so need to drain it enough to not cause a flood!
     
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  11. gasmanstu72

    gasmanstu72

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    there should be a drain point at low level (maybe on the cold feed or the cylinder) like this:

    [​IMG]

    or there could be another gate valve tied in off the cold feed at low level with a pipe going to outside,

    or there could be nothing, in that case you'll have to syphon the water out the top of it.

    to syphon it, turn off the water going to it, open the hot water taps till they stop (or in your case slow right down) then get some towels handy, undo the connection at the top, and you will get some water come out, (towels!!) put a hose (garden hose will do) in the hole at the top, shove it as far down as you can get it, run it to outside and sucky sucky long time on the end till you get water come out, and leave it to drain,
    job done!

    if your fitting a flange you'll only need to drain it past the level of where you want the fitting.

    good luck,
     
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  12. pavsid

    pavsid

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    There is a drain point, great! Thanks.

    With regards to fitting a outlet off the cold water tank, i found an outlet already there which is no longer used, so I'm thinking I can use that. However, it's a 15mm outlet, and the one I want to fit is 22mm because it's going to a shower pump. If i fit a reducer to the existing 15mm outlet, and then run 22m pipe to the shower pump, will that be ok, or does that defeat the object of having a 22mm pipe?!!
     
  13. gasmanstu72

    gasmanstu72

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    you could do, I don't think it wouldn't affect it that much to be honest, but if you're going to do it, you might as well do it properly!

    also, consider a surrey flange for the hot water, they're easier to fit in my opinion, saves cutting the cylinder, but it might mean altering the pipework on the hot draw off.
     
  14. pavsid

    pavsid

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    Well i'm just trying to avoid having to drain the whole tank. If it won't make a difference, then i'll just use the pipe that's there, but if it will, or at least might, then i'd rather do it properly. My guess is that by having a 15mm outlet it defeats the object of having 22mm pipe, as only a certain amount of water can ever enter the pipe anyway (through the 15mm outlet)...but then I'm no expert so that's just a guess! The pump instructions say the pipework MUST be 22mm, so if there's only going to be 15mm worth of water feeding it then I'll have to change the outlet to 22mm. What you reckon?

    Yeah, did get one of those originally, but the pipe work at the top of the cylinder is too tight and seems like it'll be more trouble than the essex flange. Also the pump manufacturer will only offer a 3 year warranty if their flange has been used, which is the essex one i've got.
     
  15. gasmanstu72

    gasmanstu72

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    its more for the volume of water rather than the pressure, so if you are using a 15mm tank connector it wont restrict it much.

    but, if you've got to change the gate valve that's letting by anyway plus drain the cylinder you may as well drain the tank and do it properly, it doesn't take long at all, turn off the mains and open the taps I bet it'll be drained within 10 minutes!

    edit:
    drain the cold tank first by doing what I said above, then drain the cylinder off as much as required, if you try and drain the tank and the cylinder both at the same time through the drain point it'll take ages :D
     
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  16. pavsid

    pavsid

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    You're a legend! Thank you so much :)
     
  17. pavsid

    pavsid

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    So, i've emptied the cold water tank, there's no more hot water coming out of the taps, and i'm ready to fit the flange to the hot water cylinder....except there's nothing coming out of the drain valve on the cylinder!

    I've turned it all the way anti-clockwise to the point that the nut pretty much comes off, and all that's come out are a couple of drips.

    I noticed another valve just before it too, and have undone that a little to see if that'll do anything, but again only a couple of drops came out..

    I've uploaded a photo to show you..


    Any ideas? Surely both valves aren't broken?

    Just wanted to check i'm not doing something wrong before I take the nut off the top and syphon it out...
     
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