bbeaton wrote:I posted this in the Mirca thread w/r/t Pre-Infusion on a machine running from the reservoir, but it feels relevant to post here as well.

I should rather ask you here instead - how did you measure 3bar in pre-brew?

My experience with enabling pre infusion without being plumbed in is also somewhat different from yours. I've posted this earlier in the thread:

5s Preinfusion without Plumb-In

20s Pre-Infusion Shot without Plumb-In

My mistake, good catch I'm sorry I mis-remembered the text in the app. I edited my reply to reflect that.

removed 3-bar comment, I was remembering text from the app screen and confirmed that 3 bar was an example given in the pre-infusion section, not a spec for pre-brew. I don't know what the pressure during pre-brew is.

That's really interesting that you have a different experience! I'm at work in and out of meetings so I can't review your posts but will absolutely look this evening!

bbeaton wrote:I posted this in the Mirca thread w/r/t Pre-Infusion on a machine running from the reservoir, but it feels relevant to post here as well.

Yeah totally not my experience. Water comes out of the group head, as seen in these videos:
La Marzocco Linea Mini User Experience

Keeping my discussion here and will update my comment in the Mirca thread later.

Thanks Zoobee and Jaroslav for your replies. I've spent the last hour trying to replicate the results in Jaroslav's video and I can't. I have a 2022 model up to date with the latest gateway and firmware with no modifications, using the app on an Android device.

At first I noticed that Jaroslav's brew pressure was sitting at around 2 bar with the pump off, and mine sits at zero. Another difference I noticed was that I keep my steam boiler off and Jaroslav's was on and at full pressure in the video. I tried 5, 10, and 15 sec preinfusions and didn't see any movement at the brew pressure gauge until the allocated time passed, then it ramped up to full pressure.

So then I tried bringing my steam boiler to full temp to see if that would make a difference. Again I tried setting pre-infusion to 5, 10, and 15sec within the app, and running a cycle without the portafilter in place. Same result, my brew pressure gauge stays at zero until the time has passed then ramps up.

I'm not sure

• Why my machine would be different?

• Where the pressure for pre-infusion would be coming from if there's no line pressure and the pump is off? What's generating the pressure?

In the interest of adding another data point, I did experience this once testing the preinfusion where no water came out. At the time, I didn't have a portafilter in the grouphead. Immediately following I put the portafilter in and the preinfusion passed water again. I chalked it up to "oh so it only works when the portafilter is in" which in retrospect was probably not the reason. I don't think the machine has any way of knowing this. So there's probably something to do with water cycling through the brew circuit.

bbeaton wrote:

• Where the pressure for pre-infusion would be coming from if there's no line pressure and the pump is off? What's generating the pressure?

From what I understand (disclaimer: I'm not all that knowledgeable about the workings of espresso machines) it's coming from the heat exchanger. That has been mentioned here and LM support I spoke to also confirmed.

Thank you Jaroslav & Zoobee!

Learned something new today, thanks! Your comment about the heat exchanger made me go back to my workflow. The key was that I wasn't letting my machine heat up enough to build up pressure in the heat exchanger mechanism. I was able to replicate your + others' PI experiences at 5/15/20sec intervals back to back, as long as I let the boiler rebound. I'm revising my comments here and in the Mirca thread now. It all makes perfect sense, there needs to be something to generate pressure, so you can't have PI if you're only powering on the espresso boiler. Sorry if this has been discussed before. I read a lot about the machine before buying it, but apparently not enough!

Great! And fwiw I don't think it's been discussed very much, we're all kind of in the wild west here with this (unintended) new app/firmware functionality!

AAAND I have just had an interesting experience. As many of you are aware, sometimes there are various connection glitches when launching the LM app (iphone here). Some settings may be randomly unavailable/grayed out, some may not register when you change them and you have to close out and redo them, etc. Well, I just ended up on a screen where I had access to the "enable pre-infusion" switch which is usually grayed out if "enable plumb-in" is off. So I selected it and it worked! And then testing by pulling the reservoir out mid-shot, I still had the flashing blue low-water light! So this is exactly what I would want in an update.

I closed out and opened again, and it's still set this way though you can see the "enable pre-infusion" switch is grayed out in the on position, presumably since "enable plumb-in" is off. But the preinfusion time is adjustable so I think for now I'm just not gonna touch it. Maybe someone else can figure out how to get to this "easter egg", whether some combination of launching the app, closing out, etc. But it appears the capability exists and it's just a programming issue.

It would be fantastic if LM would enable preinfusion off the reservoir. Has anyone here asked what their stance is on making this available in the future?