Water dripping through tundish - Megaflow Unvented Cylinder

Discussion in 'Plumbing and Central Heating' started by beakerone, 16 Jan 2011.

  1. beakerone

    beakerone

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    I replenished the airgap in my Megaflow cylinder before Christmas after noticing quite a lot of water flowing through the tundish.

    I noticed last week that it was still dripping whenever the hot water was heating up overnight. It is a much slower drip than before and some of the pipework underneath the tundish was leaking slightly and looked like it needed resealing.

    A plumber came today and said the drip must be because of the mains cold water valve and replaced it. He resealed the pipes and assured me all was well. On checking tonight, however, it is still dripping and one part of the pipework is still leaking!

    Do you think that the airgap didn't replenish properly before and therefore needs doing again? Any advice would be appreciated. I intend to phone the plumber in the morning to give him the good news!
     
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  3. tincup

    tincup

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    Hi
    Try replenishing the air gap again.
    If that does not work a G3 certificate holder trained to work on unvented cylinders should check this over.


    HTH
     
  4. Morris40

    Morris40

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    it could just be were it was discharging before the pressure release valve has not reseated properly, maybe a little foreign matter stuck on seating, try opening valve by turning know and let it flow and then release to see if thats flushed through foreign matter, as stated before though unless your qualified i wouldn't recommend playing around with the unvented cylinder
     
  5. rojaca

    rojaca

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    instructions for replenishing airgap are on front of cylinder. fairly self explanatory.
     
  6. beakerone

    beakerone

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    Thanks. Plumber is coming back tomorrow so I will ensure we try replenishing the air gap again before doing anything else. I'm hoping it is something simple!

    Appreciate everyone's advice.
     
  7. rojaca

    rojaca

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    really should spend longer reading posts. sorry you've already replenished gap. in which case your plumber needs to do some investigation into whats happening to the pressure and temperature of the water in the cylinder. your doing the right thing in getting the plumber back to do this for you.
     
  8. dcawkwell

    dcawkwell

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    You should be able to tell at the tap if there is too much pressure.
    Most likely the valve hasn't reseated. Open the valve a number of times
    it should reseat. If not it is a case of replacing the pressure relief valve.
     
  9. Morris40

    Morris40

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    thats just what i said 1hr 30 mins ago :)
     
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  11. beakerone

    beakerone

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    Just thought I would update on the solution (I hope!) to this problem. A Heatrae Sadia engineer came out today and advised that as I live in the flat, the hot water tap is not low enough for the airgap to replenish.

    He opened the tap on the pipe at the bottom of the cylinder and replenished the airgap this way using a bucket, but he said that it was better done with a hose from there to the bath.

    After all that, it was just the airgap but a more involved way of replenishing it than just opening the hot tap and pressure relief valve in the usual instructions. I hope this helps somebody else in the future.
     
  12. muggles

    muggles

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    Hmm the age-old air gap problem. That and the persistently unreliable cold water combination valves are among the various reasons I don't like the bl00dy things, give me a Super S any day...
     
  13. mrshr

    mrshr

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    Hi guys,
    I know this is an old thread but I think I have the same problem.

    Tundish on my megaflo has water running through it when the boiler is heating the cylinder. If I stop the boiler, the flow through the tundish stops.

    I notice the recharge instructions on the front of the cylinder says if overflow runs 'intermittently'
    But i dont think my problem is intermittent i.e. random times. Its only doing it when boiler in heating cylinder.
    Doesn't do it when only the central heating is on.

    Doesn't seem to be any other symptoms i.e. still getting hot water for baths/showers and pressure at taps is as usual.
    Its a 250ltr cylinder so dont want to drain it for recharge if you guys think that's not actual prob.

    Appreciate any help.
     
  14. If its only doing when the boiler is firing with a HW demand it is probably the air gap that needs recharging.
     
  15. mrshr

    mrshr

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    OK so you think I need to do a recharge?
    I haven't noticed any performance issues. ie. flow at taps and shower all fine.

    Does the recharge process mean all 250lts will be drained?
     
  16. You wouldn't really lose any performance. But the air gap at the top of the cylinder has been lost. So when the water is heated by the boiler it has no where to go wgen its expanding so comes out of the tundish. You shouldnt need to drain all the water. Maximum would probably be to 1/2 way.
     
  17. mrshr

    mrshr

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    Ran a recharge this morning and then ran boiler for an hour to heat cylinder. Seems the tundish is dry so looks like the recharge did the trick.

    Took about 40 mins for gurgling to stop and downstairs hot tap to stop. Does that sound right?
    How often, typically, is a recharge required?
     
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