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Bes920 dual boiler low pressure 2nd extract

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  • Bes920 dual boiler low pressure 2nd extract

    So I have noticed recently that my machine extracts at a much lower pressure on the second cup. I have never noticed this, it actually used to be the opposite.. Originally I put it down to the temperature of the system warming up thus the 2nd extract being higher.. But now its much lower.

    So if the first one extracts at 10 bar and pretty much holds that for the whole extract, the second one can be as low as 6 bar and constant.

    Volume of extract is high at 6 bar..

    Grinder is the smart grinder. Sorry don't have model number at hand, but it's the one sold with the bes920 with digital display.

    Any thoughts? My suspicion is the grind is changing? Seeing the flow is high with low pressure. But I really don't know so hope for some insights. I find it odd that it's always the second and on next cofffeee session it's back to high again for the first so this causes me to doubt its the grind changing.... Maybe I need to do more consecutive shots.

  • #2
    Are you purging any coffee through the grinder before grinding the first shot? Are you weighing the amount of ground coffee before tamping?

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    • #3
      No I'm not purging any beans through. I don't weigh the coffee no. Just relying on the timer the grinder has which I believe is fairly consistent. However I'll check.

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      • #4
        The timer is actually pretty inconsistent in terms of how many grams of beans you get each dose. Try making a third shot a few times and see how that compares. My suspicion is the stale grounds are having an effect on the first coffee.

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        • #5
          Next time, after your first shot, load the basket with the cleaning disc then run a shot as you normally would. If the gauge reaches 9-10 bar then it's your grinder at fault, it it's still low then it's the coffee machine at fault.

          If it's the machine, it'll be either the coffee pump or OPV that needs to be replaced, it's best to change them both together.

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          • #6
            I like this idea. I was actually thinking while at work about using the cleaning disc. But I hadn't thought do a single shot first, then put the cleaning disc in. Good idea.

            I will also try running the grinder to clear stail beans after the above.

            I already have a spare pump sitting here as I almost replaced it before.. But I diagnosed it as the solenoid before I changed the pump over.. So if ends up being that, well I can justify my previous purchase ?

            Judging by the sound it doesn't sound like it's hitting the opv limit (I have that set quite high @ just over 10 bar and know that sound).

            Some good advice here thanks.

            Comment


            • level3ninja
              level3ninja commented
              Editing a comment
              The pump and solenoid often go around the same time

          • #7
            So it seems that if I run the hot water before extracting the second coffee, then the pressure is normal. I always run it for the first extract anyway to warm the group head up and ensure hot water is through the system, so that seems why the first one is always good. If I do the same for the second one then it seems like the pressure is good.

            Now here's the thing that makes me curious. If I don't run the hot water before the second extract, then sometimes the pump doesn't turn during the pre infusion, like its stalled and silent. But if I open the hot water then the pump works fine.. Then i can extract a coffee with pre infusion but then the pressure are low.

            Point here is if I always run the hot water before an extract then no problems. However if I wait until I try to extract, and the pump doesn't work, then run the hot water, then the extract then comes out low pressure.

            So it could be the solenoid? That changes the flow from extract to hot water doesn't it? Ive had the solenoid go before and it usually buzzed. This all just sounds normal.

            The other weird part is the flow of coffee is high volume when the pressure is low (expected when pressures low you get more coffee under normal operating). If it was a problem with the solenoid, how do I still get a high flow that corresponds with a low pressure....

            The pump not turning over when I press the extract button in the second coffee without running the hot water makes me wonder if there is a pump problem.

            However why does hot water always work fine as soon as I open the hot water switch? Same pump isn't it? Maybe the pump doesn't turn because the solenoid isn't opening?

            Comment


            • noidle22
              noidle22 commented
              Editing a comment
              The pump is worn out. The way Breville manage preinfusion on the Dual Boiler models always takes a toll on the pumps. You have textbook pump failure symptoms. My rule of thumb is 5 years or 5k shots, whichever comes first. If I see a machine for service regardless of the fault, if it's near these limits it gets a new pump and OPV. Cheap insurance.

              Why the pump always starts when you use the hot water tap is that the machine applies full line voltage to the pump with no preinfusion interference. The preinfusion function is the problem.

              I can't explain the flow dynamics part of your question. Lyrebird probably can if he sees this and wants to answer.

          • #8
            Originally posted by PeteRepeat View Post
            So it seems that if I run the hot water before extracting the second coffee, then the pressure is normal. I always run it for the first extract anyway to warm the group head up and ensure hot water is through the system, so that seems why the first one is always good. If I do the same for the second one then it seems like the pressure is good. Now here's the thing that makes me curious. If I don't run the hot water before the second extract, then sometimes the pump doesn't turn during the pre infusion, like its stalled and silent. But if I open the hot water then the pump works fine.. Then i can extract a coffee with pre infusion but then the pressure are low. Point here is if I always run the hot water before an extract then no problems. However if I wait until I try to extract, and the pump doesn't work, then run the hot water, then the extract then comes out low pressure. So it could be the solenoid? That changes the flow from extract to hot water doesn't it? Ive had the solenoid go before and it usually buzzed. This all just sounds normal. The other weird part is the flow of coffee is high volume when the pressure is low (expected when pressures low you get more coffee under normal operating). If it was a problem with the solenoid, how do I still get a high flow that corresponds with a low pressure.... The pump not turning over when I press the extract button in the second coffee without running the hot water makes me wonder if there is a pump problem. However why does hot water always work fine as soon as I open the hot water switch? Same pump isn't it? Maybe the pump doesn't turn because the solenoid isn't opening?
            What have you got your pre infusion set on? I found mine didn't work properly at the lowest setting so just turned it up one setting at a time until I found the lowest setting that would work without fail. I've read somewhere that it's a little quirk of some machines and replacing the solenoid won't fix it as it's more to do with the control settings.

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            • #9
              Turn your preinfusion settings up to 75%, if that works you'll get another year or so out of the pump most likely. If that doesn't work it's close to dead.

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              • #10
                This is good news re pump...

                I actually bought a pumo a while back and have it sitting somehwree when I had solenoid problems. I have in the past changed pre infusion settings, likely because the pump has been on its way out for a while it seems..

                Very helpful advice here. I'll try with the pump change first seeing I have one. Then look into the solenoid if it's not solved, however my solenoid is only a year old or so.

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