Bret wrote:... a brand new machine may have clearer flow paths while used machines may have had some degradation, scaling, etc that caused the pump to work harder (higher pressure).
That sounds very plausible.
...Have you confirmed with a blind basket (or the silicone disk used for cleaning) that your pump pressure gets to around 10bars? If that is good, I'd leave it be.
With the silicon disc it's 9.5. The older machines were 10, but that's because I'd adjusted them to that. I was hoping not to have to open up my new machine until at least the warranty period has expired. But 9.5 is ok yes?
For the OP: you are using the same coffee and same grind -- is there a chance that the coffee is literally the same bag you were using with the previous one, and has aged in the meantime?
The coffee is my own home roasted, which is a source of variation(!), but this was the same batch, and on the same day.
JayBeck wrote:There is some variation in Breville flow rates. My guess is your older machines pumped water closer to 8 ml/s and your newer one is closer to 6ml/s. Lower flow means a finer grind is needed.
I can't get my head around why that would affect it in that way, but I'm happy to believe you! I replaced the pumps in the older machines with the ULKA EP5 as the originals just gurgled and didn't pump during pre infusion. Is that the same as the original Breville supplied pump? Have they changed them since the early days of the BES920?