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F&E Tank Overflow query

Discussion in 'Plumbing and Central Heating' started by AshtonM00, 8 Oct 2021.

  1. AshtonM00

    AshtonM00

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    Hi there,

    So I have learned a lot about my plumbing over the past few weeks after discovering the float valve in my Cold Water Storage Tank was faulty (gushing out the overflow). I came across numerous helpful threads on this forum & I now know the difference between the CWST & the F&E header tank & generally how it all joins up!

    Anyway, since the float valve in the CWST was replaced, it got me thinking about the overflow in the F&E header tank. From what I can see, there is only 1 single overflow pipe (coming out the roof eaves), which is connected to the CWST only. I noticed on some forums, many people suggest the 2 are occasionally linked (one-4-all overflow pipe) or in some older setups, the F&E tank overflows into the CWST then continues out the CWST overflow (which is not ideal).

    I had a nose around the F&E tank & I actually cannot for the life of me see where there is an overflow pipe coming out of it full stop. It seems to have 3 pipes going into it, which I assume (again from reading over forums!) that they must be:

    * Mains water feed (at a low point in the tank)
    * Flow pipe to boiler (I think relatively low but at a higher point)
    * Vent pipe to boiler

    The tank is in a rather awkward position, which is a shelf adjoined to the roof joists/rafters directly above the CWST, but from what I can see, there really doesn't seem to be any sort of obvious overflow.

    There is a inverted "U" shaped pipe leading into the top of the CWST but I presume this is the vent/expansion pipe for the Hot Water Cylinder & unrelated to the F&E tank?

    Would I be correct in assuming because the water main enters low down in the F&E tank & it's the highest point in the house where water main travels, it cannot (due to gravity or some such) fill any higher than it's highest point? Thus cannot overflow? Or is that absolutely not the case & there absolutely should be an overflow?

    Sorry for the waffling above but trying to be as detailed as I can in the first post.

    Just again for clarification, the F&E tank is above the CWST & the mains cold seems to T into both of them.

    Any thoughts appreciated!

    Ash
     
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  3. JohnD

    JohnD

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    Photos please.
     
  4. AshtonM00

    AshtonM00

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    Will get some uploaded when at home (in Office at the moment). Thanks for coming back to me.
     
  5. denso13

    denso13

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    Yes, the cistern should have an overflow.
     
  6. fixitflav

    fixitflav

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    Surprised the fill pipe enters low down, usually it's above the water level. And there must be a float valve (similar to a toilet cistern).
    No, that's not right. If it has enough pressure to reach the tank, it has enough to potentially overflow.
    Yes there should. What's the F/E tank material? If it's plastic it shouldn't be too much trouble to fit one. Routing it into the CWST may not be ideal, but I don't see a problem.
     
  7. denso13

    denso13

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    You don't really want to be bathing in the crud and inhibitor from a CH system
     
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  8. terryplumb

    terryplumb

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    I suspect fixitflav was referring to connecting to the cwst' overflow pipe ,not into the tank itself ,which wouldn't be wise at all.
     
  9. Hugh Jaleak

    Hugh Jaleak

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    Pipework should be going from bottom to top, Feed to CH system, Cold feed and then Vent pipe going in over the top in an inverted U shape.

    No harm in commoning the overflow pipes below the outlet level of the lower cistern, having one discharge into the other before overflowing is not recommended, and just laziness on the part of the installer.
     
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  11. fixitflav

    fixitflav

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    Since it may never happen, and if it does perhaps once in 10 years, I can't see much of a problem. But as I said, not ideal, and now you mention it, teeing into the CWST overflow is the best way.
     
  12. AshtonM00

    AshtonM00

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    Hi all,

    Thanks for your responses. I will get some pics anyway as I may have got the entry order of the pipes wrong, but it definitely doesn't seem like there is an overflow. Both tanks are plastic.

    I think this is a case of the old Chinese proverb "those who ask for advice already know the answer but wish they didn't" !

    Would you think this would have just been laziness of the person who originally installed it all? I would have thought an overflow would be an absolute critical part of an installation!

    Ash
     
  13. terryplumb

    terryplumb

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    Let's see the pics. If there is no overflow from the f&e , its anyone's guess as to why the installer hasn't provided one .
     
  14. fixitflav

    fixitflav

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    Does the F/E tank have a float valve? It's rare, but I have seen cases where there was just an iso valve, so the tank was topped up manually. Then maybe no need for an overflow, but have to check the level every few months.
    I had one case where there was no piped supply to the tank, and had to carry a bucket up the loft. I'm not in the trade, that was a friend of a friend, whose heating had stopped working years before because low on water and she'd done nothing about it. Filled it up and the heating worked OK, but she couldn't afford to run it and switched it off!
     
  15. AshtonM00

    AshtonM00

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    That's interesting fixitflav. It's really awkward for me to open it & look as I was tempted. It's almost like you need a small 2-step ladder but the damn CWST is in the way & there isn't much clearance above. If I really needed to open it I could though. The cold feed pipe into it has a tap handle on it rather than an in-line valve you turn with a screwdriver, whether or not that means anything! Presumably on a system like that, if one has a leak from a rad pipe or flow/return, it would run the system dry then break the boiler? *gasp*

    Ash
     
  16. fixitflav

    fixitflav

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    The feed pipe valve doesn't really tell us whether there's a float valve. It would be nice to have to isolate locally to service the float valve (if any!), rather than turning off the whole house.
    If it does run dry I would like to think the boiler would detect it and shut down, without suffering damage. Many years ago, early 1980s I had a float valve stick so the tank emptied. Can't remember the symptoms, whether the boiler made noises or just stopped, but it did no damage, and that was a very basic CH500 boiler, if you're old enough to remember them. Replaced the float valve with diaphragm type. The ex still lives there and it's been fine since!
     
  17. boringoldcodger

    boringoldcodger

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    I'd be tempted to try to turn that valve off and if it won't turn then try to turn it on and, if it moves, see if you hear water going into the tank. At end turn valve back to where it was.
    If you can turn it off then there's probably a float valve in the tank.
    If it's seized up then, unfortunately, you've probably got a whole can of worms.
     
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