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  • Scale blocking boiler pressure gauge

    Hi All,

    My two year old ECM Mechanika Profi developed a very slow responding boiler pressure gauge.

    Given that the machine was still producing good steam pressure and water temperature I figured that the gauge was either faulty or blocked.

    I pulled off the pipe that connects from the boiler to the pressure gauge and found that the opening at the boiler end was blocked with scale. A quick soak in vinegar softened it and I cleared it out with a needle.

    The pressure gauge is now behaving normally.

    Concerned that I might need to descale I removed the mushroom and found no evidence of scale at all. I live in Melbourne Bayside which has good water.

    I am now wondering whether I need to descale the boiler or just leave it.

    Any advice would be greatly appreciated.

  • #2
    I'll say yes, and further I'm guessing you don't use the hot water wand on your machine much.

    The boiler is thus effectively single ended: water goes in but only steam comes out, so dissolved solids accumulate. The Hx is double ended (water goes through on the shot) so the accumulation is much lower, hence the clean mushroom.

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    • #3
      Originally posted by Lyrebird View Post
      I'll say yes, and further I'm guessing you don't use the hot water wand on your machine much.
      The hot water wand gets used to make long blacks and cups of tea a few times per week, but not every day.

      I suppose the frequency of the boiler refill mightn't be often enough.

      I will give it a descale over Easter.

      Thank you for the advice.

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      • #4
        It's not the frequency of boiler refill, it's the fraction of water that comes out as steam, leaving its solids behind.

        If the fraction of the boiler volume that exits as steam is S and the fraction that leaves as water is W, the concentration factor per cycle is

        (1-w)/(1-s) + w

        so after n cycles the original TDS level will be concentrated by

        [(1-w)/(1-s) + w]^n.

        To give you some idea of the numbers involved, let's assume each of those fractions equals 0.1 over a period of a week. The concentration factor in a year is then [(0.9 /0.9) + 0.1]^52 or 1.1^ 52 which is about 140, so if the TDS in your feedwater is say 70 ppm* the concentration in the boiler would rise to about 10,000 ppm (or at least it would if large amounts didn't precipitate as scale).


        * this is a typical level as measured at my tap in Melbourne when I lived there.
        Last edited by Lyrebird; 30 March 2019, 05:57 PM.

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        • #5
          IF your mushroom looks good then I would guess there is no need for a full descale. My understanding is that the mushroom is a good indicator of scale level?

          It doesnt take much to block the usually very thin tube to the gauge.

          Cheers

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          • #6
            Originally posted by artman View Post
            I My understanding is that the mushroom is a good indicator of scale level?
            See post#2 for an explanation of why the mushroom is not necessarily indicative of scale in the boiler

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