malachi wrote:Never trust any in-machine gauges. They're largely meaningless in my experience.

I wouldn't go so far. I would rephrase to Trust them for what they are designed to do but be careful when yo extrapolate into areas they are not designed for.

In this case the OP has a real issue with the machine. I don't know what it is but I am fairly certain it is a leak somewhere. Large enough to dissipate pressure quickly but not large enought to prevent it from building up in the first place.

For that purpose the pressure gauge is good enough.

As others have said, this is not normal for a GS/3 because the water is trapped in the boiler when the 3-way is closed. The pressure should be in the 5-12 BAR range. It will increase a little when the heater cycles on and decrease a little as the water cools.

AssafL wrote:If pressure decreases, water is leaking somewhere. It might be any connection, 3 way valve, HX tube, flow meter, heater Oring, temp sensor, expansion valve or tubes that lead to expansion valve, etc.

In most of these cases, you should see evidence of the leak. Remove the side panels, cup tray and top cover and look for evidence of water. Also remove the drip tray so you can see whether water is leaking from the 3-way exhauset or expansion valve into the drain box. It's normal for water to come out of the 3-way exhaust after a shot or when backflushing, but not otherwise. It's normal for water to come out of the expansion valve when the pressure reaches about 12 BAR (if you have the expansion valve adjusted correctly) but not otherwise. Run the machine with the covers off for a couple of days to make sure there are no leaks.

A leak in the HX tube would cause the steam boiler water level to rise, but the leak would stop when the line pressure and steam boiler pressure equalize. In that case you would see the same pressure on both gauges: 1-2 BAR. It's certainly possible that your coffee boiler gauge is slightly defective and reads zero when the pressure is that low. The original coffee boiler gauge on my GS/3 did that after a while and I had to replace it.

The only other thing I can think of is bad check valves between the pump and coffee boiler. This would allow water to leak back through the pump into the supply. The using the reservoir, you would see the water level rise and the pressure would drop to zero. But when plumbed in the coffee boiler pressure should equalize with the line pressure. What's your line pressure? This scenario is unlikely because there are at least two check valves in the line. One is at the pump and one is at the entry to the mixing valve. Not sure if there's another one in the path. If it's the check valves, it would almost certainly have to be caused by debris in your water lodging in the check valves and keeping them from closing. It's imperative to use a water filter between the input supply and the GS/3 to avoid this. Do you have a filter inline?

My educated guess is that your middle o-ring is tired . . . very tired. You made a mistake in tightening up the expansion valve. This valve should be set to drip . . . drip . . . drip when the brew boiler pressure is 11-12 bar. The methodology called out in the LM manual is simply a PITA. Adjust the pump to ~11.5 bar and adjust the expansion valve as appropriate.



The pic above shows the shaft position in the exhaust (or off) position, i.e. all the way to the right.

I removed both side panpels and cup tray, running through the machines thoroughly while the machine was cool, can't find a singe drip of water stain. The machine was completely dry including the drip tray.
Could it be any other issue besides leaking? If pressure gauge is showing 0 but I have a constant 2 bar line pressure to the machine, it has to be a big leakage somewhere. But I can't detect any of that and the pump is running with the pressure set earlier, 9 bar when brewing and also blind filter.

How quickly does the needle return to 0? When my 3way valve seals were due for replacement you could see the needle going from 9 to 0 gradually over the course of around 2 minutes.

Once I stopped the brew at the set pressure 9 bar, it wil drop to 0 in less than minute.
What is your symptom of the 3 way valve seals issue? I used to have water dripping from my group head and 3 way valve but issued resolved after replaced the 0-rings. That was 5 months ago. Now I can't find a single drip everywhere when the machine is cool with constant line pressure of 2 bar.

I have volumetric GS/3, so I'm not very familiar with the o-ring and exhaust system in the MP. But from your description it sounds like water is escaping from the boiler very quickly after the shot -- as you say, within two minutes. You mention a dry drain box, but it should be wet just after you pull a shot and the pressure is relieved in the portafilter. Are you sure that additional water isn't flowing into the drain box after you pull the shot?

Try this: Watch the group exhaust on the left side of the drain box as you pull a shot and for at least two minutes after the shot. At the end of the shot, you should see water shoot out of the exhaust as pressure is relieved in the portafilter. If water continues to flow out of the exhaust, then it's likely that the you have one or more bad o-rings in the group head.

That said, I would think if the o-rings are leaking, and you really do have 2-BAR input pressure, you would see water flowing into the drain box continuously.

Are you absolutely sure your input pressure is 2 BAR?

At this point, I wouldn't rule out a defective boiler pressure gauge.

The drain box was completely dry when the machine was off for 12 hours. Just to ensure no leaking from the 3 way valve due to the O-rings. I can't find any sign of leakage.
Like normal, when pulling the shot I can see the water access from the 3-way valve after I stop the pump.
To my understanding, I should see at least a minimum pressure from the brew pressure gauge when plumbed in but not completely 0. I can confirm that my water source is connected to the pump with some pressure. My pump is smooth and soft when drawing hot water.
Also when the I turned on the machine and started to heat, I don't see any movement from the pressure and no water escape from expansion valve. I should see the pressure move up to 12 bar when heating. But the needle just stay at 0 and my brew temperature was set to 95c.
I tested with the blind filter and the static pressure did shows up at 9 bars when brewing.

Another thing to mention, when I draw the hot water, the pressure will goes up to 9 bar and back to 0 when stop.
When the pump is refilling water from the source, I can see the brew pressure move to 2.5 which I assume is my line pressure.

erics wrote:My educated guess is that your middle o-ring is tired . . . very tired. You made a mistake in tightening up the expansion valve. This valve should be set to drip . . . drip . . . drip when the brew boiler pressure is 11-12 bar. The methodology called out in the LM manual is simply a PITA. Adjust the pump to ~11.5 bar and adjust the expansion valve as appropriate.

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The pic above shows the shaft position in the exhaust (or off) position, i.e. all the way to the right.

eric, are you suggesting me to loosen the expansion valve? I did not change anything and the boiler pressure used to stop at 12 and drop to 3 when heating. Now the boiler pressure needle just won't move when heating and no water drip from the expansion valve.

eric, are you suggesting me to loosen the expansion valve?

I'm suggesting that you readjust the expansion valve as per the manual numbers because you said that you "tightened" the expansion valve so now I'm saying it needs to be properly adjusted.

The expansion valve should be set as per the numbers in the appropriate manual (I think it is 11-12 bar) but not necessarily as they say to do it BECAUSE that is a PITA. Simply adjust the pump up to 11-12 bar when using a blind filter and readjust the expansion valve to go drip . . . drip . . . drip. Now, start all over again and readjust the pump to a brew pressure of 9.0 bar when simply flowing through an empty basket. Setting the expansion valve on a rotary pump machine should be done ONCE and maybe checked every three months or so. It is simply functioning as a "thermal expansion safety valve" on the brew boiler hydraulics. For the purposes of troubleshooting this "problem", I would suggest you simply draw from the reservoir until the "problem" is solved.

The GS/3 is SOMEWHAT unique in that the brew boiler is fed water from a hx in the steam boiler. The temperature of this feed water is adjustable (not for the typical user to do) but that brings up other factors that are really beyond the scope of this thread. You could easily be feeding the brew boiler with water that is equivalent to the existing brew boiler temperature and thus the heating element duty would be zilch.

Start up a room temperature machine and immediately flow about 4-6 ounces from the group. As the water in the brew boiler begins to heat, it expands and raises the pressure to the point of very slightly opening the expansion valve (as others have said). You say that you experienced this very action. If you do not see this rise in pressure under the EXACT conditions I have described, you either have a faulty gage (Dick experienced this) or a leak . . . plain and simple. Given all that has gone on in this thread, I now suspect a faulty gauge.