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Potable water expansion tank

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  • 19-01-2019 11:38am
    #1
    happylad
    Registered Users Posts: 211 ✭✭


    Hello
    I have recently noticed that my pump for my showers etc comes on even when we are not using it. It might only run for 10/15 secs. Also when we do want to use the showers or flush the toilets there might be a delay on the same amount of the time before it kicks in. It works away fine when it does kick in.

    I checked the 25ltr expansion tank we have on the system (blue) and it appears to be filled other water. I am going to change this out and put a new one in. They come precharged to 4bar. Our system works at 2bar.

    Should I change the precharge pressure to 2bar or is 4 bar ok.

    Thanks for the help


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    #2
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    happylad wrote: »
    Hello
    I have recently noticed that my pump for my showers etc comes on even when we are not using it. It might only run for 10/15 secs. Also when we do want to use the showers or flush the toilets there might be a delay on the same amount of the time before it kicks in. It works away fine when it does kick in.
    vale
    I checked the 25ltr expansion tank we have on the system (blue) and it appears to be filled other water. I am going to change this out and put a new one in. They come precharged to 4bar. Our system works at 2bar.

    Should I change the precharge pressure to 2bar or is 4 bar ok.

    Thanks for the help

    Are you changing it because because there is water coming out of the schrader (air end) valve? If no water or air pressure then it probably only needs pre charging, see below.
    The fill pressure should generally be set ~ 0.3 to 0.5 bar lower than the pump cut in pressure, if you don't know what that is then I would suggest setting it to say 1.5/1.7 bar. Under no circumstances leave it at 4 bar as that is the same as having no E.vessel or having it filled with water due to a ruptured diaphragm or having lost lost all the pressure out of the air end.

    The reason for having it set below the pump cut in pressure is that there will be a small water reserve in the E.vessel which will help to stop the pump cutting in constantly.


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    #3
    happylad
    Registered Users Posts: 211 ✭✭happylad


    Thanks for the reply. Yes water is coming out the valve.
    I will adjust slightly below the 2barg operating pressure.

    I must also check the pressures in the HW expansion tanks. System is working at 1.5barg. Is the same true of these slightly under the operating pressure


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    #4
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    happylad wrote: »
    Thanks for the reply. Yes water is coming out the valve.
    I will adjust slightly below the 2barg operating pressure.

    I must also check the pressures in the HW expansion tanks. System is working at 1.5barg. Is the same true of these slightly under the operating pressure

    Yes, although its amazing how many, even boiler manufacturers advise the pre pressure and charging pressure as the same, it leads to more frequent top ups as there is no water reserve when the boiler is cold, of course someone came up with the auto fill valve which is a pressure reducing valve left open all the time and can lead to expensive radiator replacement because if there are any small leaks then they are masked by the auto fill function. With a small 1 to 2 litre reserve then you may only have to top up once a year or so and if the top ups become very frequent you know you have a problem and can deal with it.


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