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Breville BES860 pulsing and pressure loss
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You primary issue is a failing pump, very common on older or high use machines. They will usually work just fine when under no load and show a fault when at or near maximum pressure.
There's also a small inline water filter between the water tank and flowmeter, best to check that as well and make sure it's clear. If they get blocked up it can cause havoc with extraction consistency. Your pump will still need to be changed though.
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Breville BES860 pulsing and pressure loss
Hello wise coffee-people
My trusty BES860 (8 yrs) suddenly started having pressure problems about a month ago. Your advice would be appreciated.
The main symptoms are pulsing, and unusually also pressure loss, which is why I'm not sure if solutions to other people's problems apply here (all vids I've found only show pulsing with no decline in extraction/pressure; the same with forum reports I've read in various places).
Normal (old) behaviour for my machine: pump reaches pressure during extraction, needle stays stable at one point (close to 12o'clock on the dial). If the coffee is much too fine/too full, the needle would hit one-o'clock and either pulse a few times, or just hold at that point on the dial while extracting a few drops.
New behaviour:
Coffee at my normal grind and fill: pressure builds quickly to approx one o'clock on the dial (higher than usual), pulses once or twice (ie, the needle fluctuates by two or three "hours" on the dial), and then immediately declines to almost zero with pump still running quietly. A short burst of coffee-flow before the pressure drop, then intermittent little drips until the pump stops.
Grind tweaked to be coarser: coffee flows quickly (as would be expected for a coarser grind) and the needle goes high (unexpected), then bounces 2-5 times, but lower on each pulse, then declines to almost zero and continues as above.
Grind/fill/tamping tweaked further over recent weeks: I've kind of found a sweet spot where the machine will mostly behave as above, but just keep bouncing until the shot is done if I'm lucky (the peak of each pulse is "1o'clock"-ish, but the needle falls a little lower at the end of each pulse), rather than pressure declining to almost zero.
Steam: seems a little weaker. Occasionally (but I can't reliably reproduce it) there is minimal steam produced (it just sits there with no pump sound), but mostly the steam (and pump) does work adequately to froth milk well.
Other symptoms: I have the feeling the pump sounds slightly different, but not enough to be certain.
Of the videos I've seen, this one is most similar in the intensity of the pulsing, but differs in that there is no decline in pressure at the end of each pulse.

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