Cold water tank overflow dripping like mad

Discussion in 'Plumbing and Central Heating' started by JackDashed, 19 Dec 2007.

  1. JackDashed

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    I'm a complete plumbing novice so please forgive me if I don't explain this quite correctly.

    In my loft are two tanks. Going into the larger is a fairly thick pipe that rises above the tank and then enters the tank, from above, through a hole in the lid. I am guessing this was once connected to a water boiler (we have a combi now).

    Going into the larger and the smaller (and I'm guessing the smaller feeds my radiators) are thinner pipes, each with a brass tap-like attachment which, I assume allows me to prevent water leaving the tanks.

    The problem I have is that the overflow pipe that comes out of the loft just below my roof drips quite rapidly. This evening my wife took a shower and, rather than decrease the drip, water just flowed out of that pipe onto the flat roof below. It went back to a rapid drip once she had finished.

    I assume the solution might lie with the water control valve inside the big tank but two things concern me:

    1. I can't get the bleedin' lid off because the boiler pipe goes into the tank through a hole in the lid preventing the lid from lifting off. I'll probably have to slice the lid with a stanley knife so I can remove it. Unless I'm missing a trick here...

    2. But I baffled as to why the flow through the overflow pipe increased when my wife was drawing water out of the tank for her shower. I expected the dripping to stop - not become a free flow!

    Anyway, could any knowledgable person offer their two pennies' worth and tell me what they think is happening with my overflow and what they reckon I need to do to cure it.

    Many thanks,

    Jack
     
  2. JohnD

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    you have a combi? Most likely no hot water cylinder then? So what do the tanks do? Combis are usually sealed and do not need a tank to keep them (or the radiators) topped up.

    What does the pressure gauge on the combi show?

    Is the filing loop turned off?

    Is your cold water at mains pressure, or tank-fed?

    Is your hot water at mains pressure, or tank-fed?

    Do you have a shower pump?

    If you do have a cylinder (which is an excellent way to provide hot water) it might have an internal leak. how old is it?
     
  3. JackDashed

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    Hi John,

    Just keep in mind I don't know one end of a rising main from another...

    By 'combi' I mean that the one boiler provides our central heating and hot water.

    If pressure is measured in 'bar' then the boiler pressure seems to be 1 bar.

    Could you help me locate the filing loop? I don't know what it is.

    My cold water upstairs comes from the tank in the loft while the cold downstairs is, I believe, from the mains.

    No, no shower pump. We do have a shower/toiler/basin in the loft but the cold is mains fed (I think) and the hot comes straight off the ground-floor boiler.

    Thanks John - I hope I haven't muddied the waters further!

    Jack
     
  4. ChrisR

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    SOunds like you have a bit of a hotch potch.
    If your shower is fed from the tank in the loft (cold) then its power would be pretty low on cold only. Is it?
    If it's mixed with hot from the combi (mains feed) then you would have something of an imbalance which would often cause problems.

    But it would explian you symptoms.
    If your HW in the shower mixer (or any mixer tap) is fed from the mains and the cold is from the loft, then hot will force its way back up the CW pipe and overflow the tank. I expect at this time of year you don't need to mix any cold with your combi's hot, so that's what happened.

    Proper answer is to get your plumbing sortedout so everything is off the mains. You could keep the loft tank for the loo if you're worried about the mains failing!

    The water regs require that you have non-return valves in your mixer supplies, but that's only part of your problem.

    Your combi's radiator water (separate from the tap water), could be from the mains via a filling loop, OR from the small tank in the loft.
     
  5. JackDashed

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    Chris,

    Thank you.

    The cold water power in our shower isn't the strongest - you're correct there. And getting the right hot/cold mix through our shower mixer taps is pretty difficult - we usually end up scalding ourselves.

    Would you mind just explaining a little further how hot water manages to go up the cold water pipe? I assume (undoubtedly wrongly) that the cold half of the mixer tap receives its cold water via a pipe that leads directly to it from the loft tank - or , if not directly from the cold water tank at least from a pipe that itself comes from the cold water tank.

    The hot tap, on the other hand, I believe is fed from another source starting downstairs at the boiler.

    I would have thought these two feeds - one hot, one cold - don't meet until they pour out of my taps. How does hot water get up the cold water pipe?

    We do in fact need to mix cold with the combi's hot because the combi's hot is scalding. Would I be correct in guessing that if we run the cold then the hot can't get up the cold water pipe? I am wondering if, for some bizarre reason, my wife wasn't running the cold tap...

    Thanks Chris,

    Jack
     
  6. JohnD

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    A Combi has no hot water storage cylinder (generally) but heats the hot tap water instantly when used so it is at mains pressure.

    A shower mixer mixes the hot and cold inside the body of the mixer. Sometimes they have an internal leak. this is how the high pressure water can force its way up the low-presssure pipes. You need a high pressure (mains) supply to the shower mixer to prevent this happening.

    There are some expensive shower mixers that can accomodate a difference in pressure between hot and cold, but not (as far as I know) as big as the difference you have betweeen tank and mains pressure. You can also get a balancing valve that can reduce the high-pressure supply but I had one of these and it tended to stick. You could give it a try as it will only cost in the £30-£50 range and is not very complicated to fit.

    With ordinary single taps, there is no mixing. And in most UK kitchen taps with a separate knob for hot and cold there is no mixing (but there may be leakage on ceramic taps with a joystick)

    I am not a plumber.
     
  7. tryitandsee

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    Can you not just put a non return valve on the cold supply to the shower.
     
  8. JackDashed

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    John,

    For a non-plumber you certainly know your onions! Thanks for your advice - I appreciate it.

    Tryitand see - I have a plumber coming today so if he agrees that water is going back up the cold water pipe I will suggest this to him.

    Many thanks to the people who have offered suggestions - I am very grateful.

    Jack
     
  9. tryitandsee

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    Great, let us all know how you get on.
     
  10. JohnD

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    you mentioned it is dffcult to get the hot/cold balance right. A non-return will not help with that, but a pressure balancer (or, better, a new cold pipe from the mains) will.

    Most people who have combis like to remove the cold tank and run everything off the water main. this is OK unless you have several bathrooms or other calls on the water, or in the very rare case of a water supply failure
     

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