Cold water tank overflowing with hot water

Discussion in 'Plumbers' Talk' started by Tiago, Oct 8, 2019.

  1. terrymac

    terrymac Screwfix Select

    Sorry ,can't make out what's what !!
    You most certainly have a cross connection somewhere within you're overall plumbing set up.
    Is the loft tank level now rising ?
    I would love to know where the cold feed to the pump originates ,if you definitely only have one outlet from the loft tank.
  2. Tiago

    Tiago Member

    It's a mess in there, quite hard to follow.

    @terrymac I've followed the mains pipe, I think this could be it - maybe.
    The mains fork at the ball cock entrance and the pipe returns to the pump?? IMG_2085.JPG IMG_2086.JPG IMG_2087.JPG IMG_2088.JPG IMG_2089.JPG

    If this is it, why it started happening after the pump change?
    I had a negative & positive pump, which I replace with a positive only, does this matter? (same brand and size)
  3. terrymac

    terrymac Screwfix Select

    I drew the conclusion that the pump must be connected to mains early this morning. When you opened the shower valves last night ,I assumed the tank level raised ?
  4. Tiago

    Tiago Member

    what do you mean by shower valves?
    When I opened the cold pipes in the pump it behave like before with the problem.

    also, if the pump is connected to the mains, as it looks like, that means there’s a broken mixer too right?
  5. terrymac

    terrymac Screwfix Select

    Meant shower PUMP !! So the tank level did rise ,as original problem?
    Your plumber who fitted the pump has some explaining to do. Now we know that the mains cold is connected ,via the pump ,to all cold outlets ,we need to establish WHERE it is getting into the hot pipework.
    If you have isolated the hot and cold to bath and kitchen taps , and leave isolated for a good while ,but the level continues to rise in tank ,then that only leaves the basin mixer ,the pump ( unlikely) or something else not yet discovered.
  6. Tiago

    Tiago Member

    yeah it did raise with the pump open

    As far as I can tell, the pump ppl only removed the old and fitted the new in the same pipes.

    I’ll try that experiment tonight, and see what happens. When you say a good while, how much are we talking about?
  7. terrymac

    terrymac Screwfix Select

    Long enough for you to monitor the loft tanks level ,obviously you don't see an immediate rise instantly. You will know better than me from your previous " tank watching" !!!!
    Something that bugged me from your very early pics of hot water cylinder ,is the section of vertical copper pipe thats not painted ,and has several white coloured push fit straight couplers on it. Obviously that's a lot newer than the older pipes with paint on them. Just indicative of recent work ,and not required to swap a pump. Was wondering if that was done when the pump got swapped ?
  8. Tiago

    Tiago Member

    So those were already there before the pump swap, I think they all age the time the previous pump was placed, but that’s unknown to me :(
  9. terrymac

    terrymac Screwfix Select

    Ah ,OK ,no worries.
    Although your pics today tend to show the cold to pump is mains fed ,it would be good to confirm this by trial to be conclusive.
  10. Tiago

    Tiago Member

    I’ll retest it tonight, but when I did try closing the valves under the shower and at the kitchen at the same time, the problem happened.

    would moving the pump to be fed by the water tank solve this problem?
    I’m pretty sure this pump weren’t supposed to be connected to mains by it’s specs.
  11. terrymac

    terrymac Screwfix Select

    Your right ,the pump should be tank fed. I have no idea why anyone would want to blank off the cold feed from the loft tank ,and connect the pump to the mains ,that's anyone's guess.
    Re plumbing the tanks cold feed to the pump ,would put hot and cold at the same head ( same pressure) and would eradicate the loft tank back filling. It would not alter the fact that somewhere they can mix (hot and cold ) but the loft tank wouldn't raise in level.
    If you are correct in stating that the old pump was connected to the cold mains ,then Its possible that on the original installation , with both connected to loft tank ,the pump would not start when cold tap was turned on ,due to lack of flow / start up pressure. So the installer ran mains cold to it. This of course is pure supposition,and if you decide to re - plumb cold to pump ,you may have the same issue with the pump not starting up.
    Given the fact that your problems started with the fitting of the new pump ,then at that time it begs the question ...what else was changed / added or removed ,or was it just the pump ? Only the installers can answer that question . And if I were you ,I would contact them to re visit.
    If you were happy to live with what you have ,in all its glory ,but just want to stop the loft tank back filling ,that can be done by fitting a non return valve ,on the pipe from the hot water cylinder to the pump.( the first isolator that you turned off at the pump yesterday ,its the copper pipe going to that).
    Another issue you had ,was when you had the " flood" and loft tank overflowed. The overflow pipework from the tank should have been able to evacuate the water to a drain or to a warning pipe outside that's open ended etc ,it shouldn't have flooded the flat. So that needs investigation and putting right. Imagine if you had been away for a few days ,you could have flooded everyone below you. Scary !!
  12. WillyEckerslike

    WillyEckerslike Screwfix Select

    Whatever the outcome, you owe Terry and Mike a meal out, let alone a pint.

    There are lots of helpful people on here (and I know others have contributed) however their determination to resolve this for you has been somewhat unusual.

    I suspect they've enjoyed the challenge but all the same it's a breath of fresh air after some of the banal exchanges between a handful of members that were taking place a few months ago

    This is one thread I have really enjoyed following. Thank you everyone.
    terrymac and The Teach like this.
  13. Mike83

    Mike83 Screwfix Select

    I tried to jump back on this thread the other night.
    Terry seemed to be making progress so I just butted out.

    All that’s been achieved on this thread could have been achieved in a hour or so by being on site. It’s just a process of elimination and a little investigation required.
  14. Tiago

    Tiago Member

    Totally, I was going to ask @Mike83 and @terrymac for DM they address so I can send something from amazon. They are famous between my friends as my internet super heroes haha.

    sadly I don’t know how to proceed to the fix yet, but this topic is managing to keep my hopes up
  15. Mike83

    Mike83 Screwfix Select

    If the pump works with tank fed HW it should work for tank fed cold water.

    currently as things stand with the plumbing, the cold side of the pump isn’t really doing anything. Having a main pass through the pump is pointless.

    swapping the pump from mains fed to gravity is fairly simple to do in the loft.
    This is the bare minimum that’s needs done.

    also the hot water pipework needs tidied up a little and altered at the cylinder.
    The source of the supplies mixing needs identified but the fault will become less evident or even stop when the supplies are balanced. Non return valves will also solve the issue.

    The issue with overflow spillage needs looked at.
  16. terrymac

    terrymac Screwfix Select

    WillyEckerslike likes this.
  17. Tiago

    Tiago Member

    So, if I am to plan some actions, how does this look (in order):

    1. replace the basin mixer (maybe the shower too) to see if the problem goes away.
    Independent of that going away or not:
    2. Reroute the pump to use the tank, and also add a no return valve on the hot
    3. Get the overflow pipe checked and hopefully fixed.
  18. terrymac

    terrymac Screwfix Select

    Good plan...
  19. Tiago

    Tiago Member

    yeah not close to and end yet...

    got a British Gas plumber again, explained to him that we isolated the hot water cylinder, boiler, the loop.
    Told him the pump is connected to the mains, and probably the basin mixer is broken.
    He said that if it was broken I would not have Hot or cold water from it, just one...
    He came up with a new solution so far, that is to install a pressure reducing valve in the mains that goes to the tank/pump.

    he sweared for his life this would fix the problem. Would you trust this diagnosis?

    I’m about to start looking for private quotes for this.
  20. jonathanc

    jonathanc Guest

    Pressure reducing valve is a bodge.

    the pump needs a feed from the tank: tbh you could do that in speedfit easily

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