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Discuss Weeping WC cistern siphon/flush pipe joint repair in the Plumbing Forum area at

  1. Ulsinus

    Ulsinus Member

    I have a concealed WC cistern.
    The seal between the cistern tank and siphon has started to weep ever so slightly.
    Access to the cistern is very difficult.
    I know the correct thing would be to remove the siphon, clean the seal landings and reassemble.
    However, to this I would have to get direct access to the cistern and can only do that by stripping/breaking the tiles and I don't want to do that if at all possible.
    It got me to thinking.
    Is there something I could dose the cistern with that would seal the leak?
    A cold water version of the Fernox sealer for CH pipes perhaps?
    I can leave the cistern unused for a number of days.
    Grateful for your advice and suggestions.
    Many thanks
  2. CBW1982

    CBW1982 GSR Top Contributor!!

    Hello Ulsinus,

    I haven’t heard of anything sealer wise, if it’s concealed and plastic you may have a hairline crack which could get worse. Any photos of installation, we may be able to suggest a different way?
  3. Craig Watson

    Craig Watson Plumber GSR Top Contributor!!

    I'm assuming by weeping, you mean a small trickle of water is constantly running into the toilet pan? If so, all hideaway cistern that I've came accross allow access from the flush plate to be able to remove the syphon and replace the rubber seal.
    • Like Like x 3
    • Agree Agree x 1
  4. Ben-gee

    Ben-gee Plumber Top Contributor!!

    Seriously? Either you’ve been lucky or me unlucky - I’ve had loads of cisterns where this is not possible.
    • Agree Agree x 1
  5. Craig Watson

    Craig Watson Plumber GSR Top Contributor!!

    Really? Is that more a case of the wrong cistern used for the job? I'm not talking about the ones used in furniture, the ones you fully box/tile in with the flush plate are all accessible from the flush plate for future servicing.
  6. Ben-gee

    Ben-gee Plumber Top Contributor!!

    Ah okay yes, I’m talking of old boxed/ tiled things from before the days of flush plates ( in this country).
    They probably got done in the late eighties , maybe pine t&g panelling or ceramic tiles. Often some sort of top access to service the inlet valve but flush valve involves major surgery (it will often be a syphon rather than a “dump valve”).
  7. Ulsinus

    Ulsinus Member

    Firstly thank you all for taking the time to consider and make suggestions regarding my problem.

    I don't think that it's a hairline crack.
    However, if that proves to be the case then I will need to demolished the vanity boxing that conceals the cistern and supports the handbasin. In doing so the access problem would be solved at a stroke but the cost of re-instatement would be considerable. My better half would insist that we remodel the bathroom. Something with due deference to my wallet I'm trying to avoid.

    Craig Watson
    The weeping is located at the junction of flush pipe joint nut which holds the siphon in place in the cistern. It's not a small trickle of water. It's less than that. It's not even a drip just excessive dampness. I know what you mean about '...running into the toilet pan'. So it's not that.
    There is no flush plate. The cistern is a pre-2000 one fitted with a traditional siphon.

    You're right this is one of those cisterns that you have experienced so often before the days of flush plates. Hence trying to avoid removing and refitting the siphon.

    Hence the idea of adding something to cistern that as the water seeps it out it seals the leak. Does something like this exists?

    Once again thank you all for your ongoing help and advice.

  8. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    A quality concealed cistern are fine as long as it’s installed correctly, who the manufacturer ? , pics .
  9. Ben-gee

    Ben-gee Plumber Top Contributor!!

    If you remove the pan you will be able to gain access enough to tighten the nut under the cistern which holds the syphon in place , this may be enough to stop the leak. Probably best to have someone hold the syphon still from above to stop it twisting as you tighten.
    • Like Like x 1
  10. Ulsinus

    Ulsinus Member

    In the end I managed to get access to the base of the cistern by removing the built-in cupboard to the left of the pan.

    Then with the help of a friend, who held the top of the siphon, and using a Thomas Dudley 4-in-1 Universal Toilet Spanner I managed to tighten the flush flange nut sufficiently to stop the the weeping.

    Job done.

    Thank you all for your help.
    • Like Like x 1
    • Winner Winner x 1
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