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Overflow pipe dripping cold water from unvented system

Discussion in 'Plumbing and Central Heating' started by HarryUK, 12 Jan 2013.

  1. HarryUK

    HarryUK

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    Hi

    I have a unvented system with a megaflo cylinder, over the last year I have noticed the outflow pipe dripping outside. British Gas have replace the cold water PRV and the temperature and pressure value. Each time this has solved the problem. However the water has recently started dripping again, and this time British Gas have said it is due to a faulty mixer letting cold water flow through the hot water system, and then out of the over flow pipe.

    We live in a three storey house with the cylinder on the middle floor, would the faulty mixer only be those above the cylinder i.e. on the top floor? If so I have a shower, basin and bath mixer. I'm trying to isolate the problem but its proving difficult, any advice? Is the diagnosis correct? We do live in a hard water area.
     
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  3. JohnD

    JohnD

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    the faulty mixer problem is not uncommon. It is most likely on a tap with ceramic discs and a joystick. Probably a shower.

    If you have service valves on your taps, turn each of them off for a day, one at a time, and see if the problem stops.

    Otherwise, run each of them, half heat, for long enough for the pipes to the mixer to get hot and cold. Then turn off. Feel the pipes after five minutes. The one that is letting by, there will be cold water travelling up the hot pipe and making it feel cold.
     
  4. HarryUK

    HarryUK

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    Thanks for the tip

    Do you recommend doing this on all the mixer taps in the house, or just those above the cylinder on the top floor? I thought the water was dripping into the hot water system via gravity, or could it be coming from those below or on the same floor as the cylinder.

    I was also planning on removing the cartridge from the shower upstairs and cleaning to see if this stops the problem.
     
  5. JohnD

    JohnD

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    all of them

    the taps are connected by pipes at mains pressure, so it won't matter if they are above or below the cylinder.

    the cartidge is more likely worn than dirty.
     
  6. oph

    oph

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    Anybody checked the baffles in the cylinder.

    Probobly needs re-charging
     
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  8. HarryUK

    HarryUK

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    Yeah the air gap has been reset a couple of times so I'm ruling that out.
     
  9. Scotty69

    Scotty69

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    Air gap has to be done at roughly every 6 months
     
  10. HarryUK

    HarryUK

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    Air gap has been replenished today.

    I took the two shower cartridges out and cleaned each one before putting the back in, however this did not seem to work as the dripping continued after the water main was turned on.

    However I did notice that when replacing the en suite shower cartridge and despite really tightening all four screws, there was a small stream of water shooting out of the shower mixer when turned on - could this indicate a problem with the cartridge, which could be causing the dripping into the overflow?
     
  11. JohnD

    JohnD

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    have you tried any of that yet?
     
  12. HarryUK

    HarryUK

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    Sorry forgot to mention, I don't have any isolating valves on the mixer taps, but ran each one as instructed and couldn't feel the hot water pipe getting cold, so I tried looking at the shower cartridges.
     
  13. DIYnot Local

    DIYnot Local

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