Cold water tank overflowing with hot water

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

  1. terrymac

    terrymac Screwfix Select

    That pic looks more like an inch !!
     
  2. Tiago

    Tiago Member

    @terrymac so, to the top of the ball cock thing is about 6 inches
    To the beginning of the black overflow pipe is just a little above 1 inch.

    I went there to measure!
     
  3. terrymac

    terrymac Screwfix Select

    Weird the vertical pipe looks white in my pic !!
    How's the level ,has it risen at all ?
    Is boiler still heating radiators AND hot water in cylinder ?
     
  4. Tiago

    Tiago Member

    its probably the effect from the flashlight I was holding haha

    I don’t think it’s raising, normally this would be super full by now.
    And definitely not hot water going up, as pipes are cold.

    the boiler stoped after 1 hour, I can turn it back on - going to do it
     
    terrymac likes this.
  5. terrymac

    terrymac Screwfix Select

    When boiler is on ,what is the pressure gauge reading.
    Sorry to have you running around ,but we are getting somewhere.
     
  6. Tiago

    Tiago Member

    I don’t mind running!

    it gets to almost 1
    80F4CF64-E262-4223-8BB8-2DC4753DC327.jpeg
     
  7. terrymac

    terrymac Screwfix Select

    Great. And the water in the cylinder has been heated by boiler for over an hour as well ,yes ?
     
  8. Tiago

    Tiago Member

    yes!
    It heated for an hour and then stopped, I’ve turned it back on now at the time of my previous message
     
  9. terrymac

    terrymac Screwfix Select

    After this amount of time ,if your tank water level has not risen ,and your mains cold water has been ON the whole time ,then there is nothing wrong with the boiler,non return valve ,or hot water cylinders coil.
    What you do have is a cold mains connection to the hot water pipework. So one of the mixer taps ,shower ( remote possibility )or some other cross connection ( more remote possibility).
    What I want you to do now ,is close both isolation valves on the cold side of the pump ,so cold into pump and cold out. Then open the hot to pump ,the one you closed hours ago.
    Leave everything else as is.
    I now expect the water in loft tank to start to rise.
     
  10. Tiago

    Tiago Member

    I’m running the experiment, but I can’t confirm it yet - which is odd, it usually happens quicker than this, but I’ll give it another 20 mins to double check.

    if it doesn’t happen, does it mean the thing is cursed?

    In the case it happens,
    I did isolate the bathtub mixer early today, and it still happened, that leaves only the bathroom sink tap left, or a weird connection somewhere else, which is not impossible.
    Is it mandatory for the sink to be connected to the mains for this to be true?
    Because it’s served by the pump, but when the mains are open (pump off) the pressure is bigger - also true for the bathtub one.
     
  11. Tiago

    Tiago Member

    @terrymac it doesn’t seem to be happening.
    I don’t know if this is good or bad, but the tank seems to be quite the same.

    the guilty pipe in the cold water tank is also not hot.
     
  12. terrymac

    terrymac Screwfix Select

    Is it the hot ,or the cold that has more pressure with mains on and pump off ?
    And to be clear ,if pump and mains are turned off ,and you run bath COLD setting and basin Hot side of tap running they should both give water for several minutes ,albeit very low flow ,Do they? And if you left them running and turned the cold mains on do they both ,IMMEDIATELY ,give increased flow rates ?
     
  13. Tiago

    Tiago Member

    Pump cold switches off, and mains open:
    In the kitchen, cold has more pressure.
    In the bathroom basin hot had more pressure.
    In the shower, cold is almost dead, very very very low.

    Same setup, but mains off:
    Basin hot runs the same way, cold got dead.
    Bath hot the same, tiny drops and dead
    So they give hot water, but not cold apparently.

    I’ve opened the mains and the basin remained dead, bath started dripping

    I did all this with those switches in the cold pipes of the pump off. Should they be on?
     
  14. terrymac

    terrymac Screwfix Select

    Sorry ,my question was of historic nature ,I didn't expect you to do a trial now ,with the pumps colds isolated.
    Anyway ,if loft tank level still has not risen ,open both colds on pump ,so all 4 pumps iso valves are open . check loft tanks levels ,and while you are there ,see how many outlets there are at the bottom of the loft tank.
     
  15. Tiago

    Tiago Member

    same run, but with the pump cold switches on now (power off)

    Mains off:
    Basin hot still have more pressure, cold is very low.
    Bath hot has more pressure, cold very low

    Opened the mains:
    Bath that was in cold get loads of pressure,
    Basin hot doesn’t change visibly
     
  16. Tiago

    Tiago Member

    There are two pipes out, but one is a dead end.
     
  17. terrymac

    terrymac Screwfix Select

    Eh ? Are you sure ?
    Where is the cold feed to the pump ?
     
  18. terrymac

    terrymac Screwfix Select

    That's a sure sign that the mains is getting in somewhere.
    Getting a bit late ,but if you are up for it ,pics of pipework beneath bath and to mixer.( bath mixer )
    And when mains is on does basin cold flow increase ?
     
  19. Tiago

    Tiago Member

    The cold basin flow increases with the mains open.

    Here are soMe pics from under the bath:
    61C17E0F-78CF-4109-923A-490CEEC42BB0.jpeg D5595E19-3CDE-49A0-9A50-F38F1CD374C9.jpeg B4DD09EB-3C7E-4850-A71D-6C94F96DCD40.jpeg E34379FF-B0C9-49A1-84B3-DCB2D41EFCB3.jpeg
     
  20. Tiago

    Tiago Member

    Damn, I really don’t know why it rotates all images automatically when I post
     

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