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Discuss Hot water flowing out of electric water tank through pressure-release/overflow pipe? in the Plumbing Forum area at

  1. DaveCade

    DaveCade New Member

    Hi guys,

    I'll try to describe my issue as best I can but I've attached a video and linked to some images below that might do a better job of explaining. Edit: Just noticed the video didn't upload. I'll try to upload to an external site and pop a link at the bottom when it's done. In the meantime look at picture 3 and you can see where the water if continuously flowing through - it's the diamond shaped, open black bit of "pipe" on the bottom-right of the image.

    I've done as much research into electric HW tanks as I can (I'm a programmer not a plumber) in an effort to understand what is going on but I'm still not sure. Please forgive me if I use incorrect terms or get things dead-wrong. This whole "issue" might be perfectly normal and not actually an issue at all for all I know.

    We moved into a new rented property about 3 months ago. The property has an electric water tank for the HW system. No CH as we only have electric heaters. Since we've moved in everything has been fine but yesterday I noticed (what I think is) a new phenomena. I could hear running water coming from the cupboard housing the HW tank. I've definitely not heard this before in the 3 months we've been living here.
    Upon investigating I immediately saw hot water streaming out of what I think is some sort of pressure-relief or overflow pipe (see the linked video for reference). I don't know where this pipe goes to and I've not seen or heard this happen before (and it's a noticeable sound). It happens now every time the water has been heated/is being heated.

    There is an expansion tank (I think that's what it is?) attached to the wall above the main tank (visible in the linked pictures) which is connected to it via the same pipe system that is feeding this pressure/overflow pipe thing, in kind of an upside-down T-junction affair. Judging by the temperature of the pipes no HW is getting to the expansion tank at all. The pipe is stone cold where it goes up to the expansion tank but hot everywhere else, implying all the hot water is going straight through the pressure/overflow pipe... and off to regions unknown.

    I tried calling it through to the rental agency when I discovered it but they neither answered nor returned my messages and now they're closed for the weekend. Our rental agreement allows us to arrange our own maintenance in emergency situations and bill the agency for it, but if we do that for a non-emergency then we have to foot the bill. So, what I would like to know is; which one of the following applies...

    1) This is not a problem and I'm just an idiot worrying about nothing. If so then great - job's a good'un.

    2) This is a problem but it's not an urgent one - as in; it's not something that will cause any immediate damage or drama and won't cost us anything (in terms of high water bill for constantly running water etc.) If so then I'll wait until Monday and the agency can send maintenance around at their leisure.

    3) This is a problem!! As in; it's either going to cause some damage somewhere or it's going to hammer our water bill whilst it's happening etc. If so then I'll call an out-of-hours plumber and bill the agency for it.

    Thanks in advance guys. I appreciate any help/advice you're willing and able to give.

    IMAGES: Hot water flowing out of electric water tank through pressure-release/overflow pipe?
    Last edited: Jun 8, 2019
  2. bogrodder

    bogrodder Plumber GSR

    Turn off the electricity to the cylinder and don’t use until a G3 qualified engineer has sorted the problems, yes that means no hot water.
  3. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    either 2 or 3 if been installed correctly then 2 if not 3 but who ever works on the system needs to be g3 qualified (unvented)

    also might be worth asking when it was last serviced needs to be once a year
  4. DaveCade

    DaveCade New Member

    Okay thanks guys. I've already turned the electricity to the water tank off but it's not stopped yet. Is it likely to stop once the water in the tank cools down, or do I need to turn off the water completely (cold too)?
  5. DaveCade

    DaveCade New Member

    Edit: Apologies. Accidental double-post.
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    only way your going to get it to stop running is by turning the water supply to it off and prob the whole flat
  7. DaveCade

    DaveCade New Member

    Okay thanks again. That's unfortunate - especially as we have visitors staying with us for the weekend! Such is life though. We'll fill some buckets etc. and make do.

  8. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH I would leave the water on but keep an eye on it
  9. DaveCade

    DaveCade New Member

    If I leave it on is it likely, at least as far as you're able to tell from my rubbish description, to waste a lot of water (as in appreciable jump in water bill for the sake of leaving the water on until morning)? I appreciate that might be hard to answer. I'm only asking as we're on a very tight budget so I have to take these things into account.

    On the up-side I've now found out that "diamond shaped, open black bit of pipe" I so-expertly described is called a tundish. You learn something new every day and all that :D

    I'm going to use the agency's emergency line first thing in the morning and ask for a G3 certified engineer to attend. I figure no hot water justifies them footing the bill for it. Hopefully, anyway.

    Thanks again for your advice.

    Edit: If it helps the hot water has now stopped flowing through the tundish. As said I've already turned the electricity to the tank off but not yet isolated the water supply completely so can I gauge from this is should be alright to leave the cold water on for now?
    Last edited: Jun 9, 2019
  10. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    So there’s no water running through the tundish

    Yes this is great news you can leave the water on with no wastage but you won’t have hot water but I’m sure you can manage until you arrange with the maintenance team
  11. DaveCade

    DaveCade New Member

    Not at the moment no. The flow dropped off then eventually stopped. Seemed to coincide with one of our visitors using some of the remaining hot water before we turned the water supply off.

    Excellent. Hot water we can do without for now no problem.

    Appreciate your help once again.
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Your fine for now then
    • Like Like x 1
  13. Darren Jackson

    Darren Jackson Plumber GSR

    The whole idea of a tundish is to give a visible warning that something is wrong & needs attention. You are right to turn off the electric to it and report it to your agent.
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