Hot water cylinder vent pipe overflow

Discussion in 'Plumbers' Talk' started by Mack Eater, May 15, 2006.

  1. Mack Eater

    Mack Eater New Member

    Got the CH off (so diverter valve supplying hot water cylinder only), the thermostat strapped to the cylinder set at 65 degrees - this works fine as I've moved it up/down and system fires up/shuts down as expected. Boiler is set to level 1 of 5, pump on level 1 of 3. Water dribbles out of the hot water cylinder vent pipe a couple of times every day - not very much water, but it causes the overflow from the cold water tank (in loft) to come into play for a few mins every time. Anyone have an idea what might cause this?
  2. M.I.G.

    M.I.G. New Member

    is this a recent problem? has it worked ok in the past with the system set-up this way?
  3. Gasleak

    Gasleak New Member

    Two main reasons. First is that the pipework configuration is wrong and unless you have changed something then this is unlikely. The second is that you have a sludged up system causing a partial blockage making the open vent the easier route for the water to follow.
  4. Mack Eater

    Mack Eater New Member

    It's worked ok for some years, started occuring about 6 months ago.

    I don't see how sludge could be a cause here as we are talking hot water cylinder only?

    Haven't changed any pipework myself, any work done has been performed by a pro - last change about 4 years ago.

    Someone mentioned to me today that the coil in the cylinder can crack, increasing the volume of water in the cylinder - dunno how I would check for this though...
  5. barnet bill

    barnet bill New Member

    The coil can split but you would have water coming out the vent more than twice a day if it was that.
  6. M.I.G.

    M.I.G. New Member

    your boiler/stat/pump settings are wrong, the settings I'd have are-

    boiler stat - no 4.

    cylinder stat - max 60 degrees.

    pump - at least speed 2.
  7. Dereekoo

    Dereekoo Member

    Had a similar problem. The top water level in your header tank is to high so that when you get the dribble of water into your header tank (due to hot water expansion when heating up) it is enough to cause the water level to get up to the overflow. The water level is to high because the ballcock is set wrong (not likely as it was OK before) or the the ballcock washer is worn so that the water level in the tank rises until there is enough pressure on the washer to seal it (this was my problem and I found by changing the washer I solved the problem)Possible solution without changing washer is to bend your ballcock rod further down. You can check if this is the case by turning off the supply to your header tank and if you do not get water overflowing after a couple of heating cycles then this proves the above(but remember to turn supply back on after testing until you sort the problem)
  8. Dereekoo

    Dereekoo Member

    Oh, and pb is talking ****.Put your boiler setting at whatever you fell ok with, your stat setting to how hot you want your water (I like it at 70 so I can get a bath full of steaming hot water) and the pump is set at the lowest possible setting which gives enough power to push the water around the system (trial and error)
  9. britishblue

    britishblue New Member

    dereekoo, he said Water dribbles out of the hot water cylinder vent pipe a couple of times every day.

    The hot water cylinder vent pipe is on the secondary circuit, so that unless the coil is perforated, the water in the header tank is completely separate, and the level in the header tank cannot affect the hot water cylinder vent.

  10. M.I.G.

    M.I.G. New Member

    > Oh, and pb is talking ****.


    >Put your boiler setting at
    whatever you fell ok with,


    > your stat setting to how
    hot you want your water (I like it at 70 so I can get
    a bath full of steaming hot water)


    > and the pump is
    set at the lowest possible setting which gives enough
    power to push the water around the system (trial and

    and yet more b0llox!
  11. Dereekoo

    Dereekoo Member

    Btitishblue thanks for that, I should have read the message more closely, I guess mentioning the pump made me think of vent pipe to the heating system. I have no idea how the water can be pushed out of the hotwater cylinder so it can go above the water level in the header tank feeding the hotwater cylinder, me thinks that is hydraulically impossible.

    Pb I accept all your bolloxs but you are still wrong. If for instance the pump catergorically needs to be set at speed 2 the manufacturers would give us single speed pumps, they don't so we can set it to suit the system it has to pump against ie 1 radiator, 1 meter away or 20 radiators 50 meters away???

    As to the temerature in the tank, there is a safety issue in not havingh the water scalding hot, but if you have a small header tank, or a big bath, or the cold water feed the bath is very cold you need the water as hot as possible,

    Horses for courses, your message was to emphatic.
  12. Dereekoo

    Dereekoo Member

    Unless there is a one way valve on the cold feed to the hot water cylinder that does not allow the expanding hot water to back flow into the header tank and forces it up the vent pipe instead?? But who has heard of a refux valve on a cold feed?? And it was OK previously??
  13. Dereekoo

    Dereekoo Member

    Bend the ball cock arm in your cold water header tank lower so that the water top water level is lower. This will not stop the water coming up and out of your vent pipe but it might make enough enough spare storage capacity in the tank so that it doe not go down the overflow pipe.
  14. Mack Eater

    Mack Eater New Member

    Been away for a couple of days, thanks for all of the advice.

    Can confirm that the water is always expelled from the hot water cylinder, not the boiler vent.

    Last night monitored the system when it switched on, had CH on too this time, after about 5 mins running all pipe work was still warming up (to the touch). There was quite a loud rushing sound, which got progressively more intense, it actually sounded like a kettle boiling and I could hear unusual noises from the pipework - this noise lasted about 60 seconds only, then went quiet again. At this point the pipes were only warm, system only been active a few mins, so impossible for water to be boiling. As mentioned before, all boiler/system controls/stats are working spot on.

    Is this some sort of airlock?
  15. sooyar

    sooyar New Member

    when the water in the cylinder gets hot it expands up the open vent, and this has to be allowed for, the usual figure is 40mm per metre of head plus 150mm. so if the water level in your cold water storage cistern is say 4 metres above the bottom of your hot water cylinder, the vent pipe would need to rise 3x40 + 150 = 270mm above the water level in the cistern. If it is much less than this it could be the cause of the problem.
  16. doitall

    doitall New Member

    I love these questions and answers.

    Only two possibilities.

    A mixer valve is letting by.

    The washing machine valve is screwed.

    Check the kitchen sink tap for starters.

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