Hi there !
I was hoping to get some thoughts from those familiar with the GS3 AV.

I have a situation where i purchsed a used model produced in 08/2020. The pump makes a strained noise when running at freeflow and set at 9 bars.

When backflushing or extracting coffee the pressure ramps from 2bars (preinfusion) to 9 bars (pump settings) and then spikes all the way to 12 bars. At this pressure a heavy volume of water discharges into the drip tray through the opv valve, and the brew volume is reduced significantly, as is expected under this abherant condition

This used machine is my second gs3. My other machine was purchased new and with identical setup, it has never behaved this way.

If i loosen the pressure screw (way out) to only permit a peak at 9bars with a backflush disc inplace, the free flow pressure drops to a paultry 4 bars or so. I do not see any modifications to the machine. Its prior owner was a rental company and they know nothing about the machine.

My good machine runs 9 bars under free flow and under resistance. This is how it should behave.

Im suspecting the pump - specifically the integrated return-valve... or maybe a non-return valve elsewhere.

Seems strange that it would over pressure the coffee boiler only under resistance. I would expect additonal pressure would push the return valve in the pump more abd self equilibreate.. its as if it snaps closed and pushes full pressure to the coffee boiler. Working under free flow and failuring under resistance.


free flow of pump is 8.5 bars on both the new machine and the used one.

Backflusing or brewing with the new one i have no excess pressure over 9bars. Backflushing or brewing with the used one i get a spike to 12 bars (prior to opv adjustment it spike to 13 or 14 - i adjusted to opv to avoid stressing rhe coffee boiler)

lastly, under rest, the coffee boiler pressure falls from 9 bars to around 4 at rest, suggesting a pressure leak - though i cant be certain becuse this might just have to do with a slow closing brew solenoid.

Thoughts??

I'd check the inlet to the flow meter as it is a common place for scale to accumulate.

What is the free flow water debit?

Ive since reduced my pump pressure to 5 bars at freeflow, which gives me 9 bars during extraction. The pump noise has begun to sound less strained.

Without basket in portafilter, i yield 327mL of water in 60 seconds.



both machines have water supply pressure regulated to 40psi static 30psi running during prei fusion the machine shows 1.5 bars with an open solenoid. 4 bars with a closed solenoid. 5 bars free flow. ---this is with the pymp screw losened up to allow the pump to not exceed 9 bars under extraction.

does this seem normal to anyone? If i did t have another machine to compare it to id say this seems normal like this however my new machine runs free flow at 9bars and 9bars during extraction. Every other espresso machine ive had with a rotary pump - according to my recollection - has flowed freely and extracted at 9 bars.