Hello GS3 users, recently I bought a brand new GS3 as a replacement to my old S1, it works properly so far but I can't say it exceeded S1 but it still deserve the price in terms of the sexy appearance and its potential "variable pressure capability".
This morning when I turn on the machine and waiting for its temperature rasing, I noticed that the brew pressure always stay in zero until the temperature reading reaches ~75 degree C, then it start to raise and eventually stopped at 12Bar as the expansion valve relief the more pressure.
I can't remember when the pressure start raising previously but it should be around 50 degree C, right?
is this normal? or there's any leakage with my machine and seems to be eliminate when temperature going high?

thanks and cheers

zhaokyosho wrote:is this normal? or there's any leakage with my machine and seems to be eliminate when temperature going high?

It's normal. Unless the pump is running, the brew pressure gauge reading is largely meaningless. Brew Pressure at Rest provides a longer explanation.

to be honest I don't agree that the pressure reading in idle is meaningless, the pressure for pre-infusion is mostly coming from expansion pressure during idle, also it's a good point to observe the tiny leakage of hydraulic system.

If you mean the GS/3 AV, the preinfusion pressure comes from the steam boiler, not water expansion.

It is meaningless unless it always reverts back to zero as in this thread: La Marzocco GS3 Brew Pressure Always Zero When Idle
The pressure is rising because of the thermal expansion of the water and it should always "stop rising" as it did with you because of a properly adjusted expansion valve. What you are calling a pre-infusion is really a pre-wetting as it takes a minuscule amount of water to escape before the pressure heads towards zero.

HOWEVER, think of all of the possible variables in machines/operators/routines out there. If the brew boiler is completely full when you turn the machine on, then yes, I would guesstimate that the pressure should begin to rise at ABOUT the same temperature on one day as it did the previous.

Did you bleed the group upon initial installation?

Since this is pourover (otherwise pressure would never drop below mains pressure), another option would be that air was sucked in (e.g. water container empty).

Also, just reasoning - if water pressure (due to expansion) rose above 12bar, water would drip from the expansion valve. Upon cooling down and reheating, water volume would be less and pressure would build up slower (not too much - some water would be sucked in through the pump and check valves as water volume contracted during cooldown).