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Expansion tank overflowing - cylinder failed?

Discussion in 'Plumbing and Central Heating' started by smp50, 30 Mar 2016.

  1. smp50

    smp50

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    I've read some old threads about this and I think I know the answer already, now. Here is the situation:

    The CH expansion tank is continually overflowing (steady drip out of the plastic overflow pipe emerging from the house, plus can be seen happening in the tank itself.

    I drained water out of it until it was well below the overflow level, and watched to make sure the ball valve was still off. I adjusted it "down" as well, to make sure.

    After a couple of hours, the level had risen again and it was overflowing. When I repeated the experiment but with the feed closed to the HW and CH tanks, it didn't re-fill. When I then opened the feed to the CH tank, the HW tank refilled.


    So, I gather that the coil is leaking in my cylinder? With a house extension on the horizon I'm reluctant to replace the cylinder now as it may turn out that I need a whole new boiler setup later in the year anyway (going from five radiators and two hot taps to nine radiators and three hot taps) and my ancient baxi bermuda may not be able to serve that much.


    What do you say? Is there any way to stall the problem now, or would fiddling with levels to stop flow from HW to CH risk the opposite happening, with CH water flowing into the HW?
     
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  3. Agile

    Agile

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    That does not make any plumbing sense. Please could you read it and check and then correct it to mean what you want to say.

    As well as turning off the feed to the HW tank you should turn on a HW tap to reduce the level of the head on the cylinder.

    Can you describe the cylinder type and age?

    What are the relative water levels in the HW and CH tanks?

    Tony
     
  4. smp50

    smp50

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    Sorry - not very clear, what I meant was that when the feed to the HW header tank was closed, the CH expansion tank did not refill or continue to overflow. When the former was opened again, the CH expansion tank returned to slowly overflowing.

    In normal operation the water level in the HW tank is a good 6" above that in the CH tank. Today, they seem to be pretty much at the same mark, in line with the CH tank overflow outlet.
     
  5. Agile

    Agile

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    Well it sounds as if you do have a leak!

    With such a small level difference that could be quite a large leak.

    You risk your health from contamination of the HW water and perhaps more important rusting of the rads from oxygen in the water. You cannot add any inhibitor.

    The advice is obviously to replace the cylinder immediately.

    But if you will not do that you could cap off the heating coil connections ( on both sides ) and rely on the immersion heater for hot water.

    Tony
     
  6. smp50

    smp50

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    hmm, what's the rate of damage that could be taking place here? Will a few months ruin things?
     
  7. Agile

    Agile

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    That's impossible to guess.

    But replacing rads unnecessarily seems a risk you should not want to take.

    Furthermore it will cause sludge in the system.

    Based solely on what you have told me, I would recommend you replace the cylinder within three weeks to lessen the damage caused.

    Others may say one week or one month or one year!

    It is your choice and your risk!

    Tony


    NOTE: ALL THESE SUGGESTIONS ARE ON THE ASSUMPTION THAT YOU ADJUST THE LEVEL IN THE HW TANK SO THAT NO OVERFLOWING OCCURS IN THE CH TANK.
     
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  9. smp50

    smp50

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    You mean adjust the HW tank level downwards so that there's no pressure difference and it stops flowing into the CH tank? Do I then risk water inter-mingling in the other direction, though?
     
  10. Agile

    Agile

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    Yes, but to stop overflowing at the CH tank.

    You will not stop water flowing between the two.

    The health risk is probably small if you don't drink the hot water. But all health risks should be taken seriously.

    But your priority should be the replacement.

    Tony
     
  11. Razor900

    Razor900

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    In the meantime get the flow and returns to the cylinder capped or valved off and use the immersion. It won't be as urgent then ;)
     
  12. smp50

    smp50

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    Hi again, guys - before I go ahead and replace the cylinder, is there any final and conclusive testing I should do to diagnose that this is indeed the problem?
     
  13. Agile

    Agile

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    We have not seen your installation and a plumber might see something that you have not noticed. But that is probably unlikely.

    But sometimes we see pipework or connections which cause a problem which would not normally be fitted. That's the value of a plumber.

    Tony
     
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