Hi folks,

Relatively new Linea Micra. Over the past weeks I noticed the sound of the pump changing a bit during a shot, as if it has to work harder -- it didn't do that before. There's also been a gradual increase of water spilled from the machine into the drain tray during a shot. There used to be no excess water dumped -- but now a 30 gram shot resulted in up to 300 ml of water in the drain tray which seems rather excessive. Even when I take out the portafilter altogether, water drips into the tray when I engage the pump. No external variables changed (ie beans, grind, water, etc all unchanged).

Wondering if this sounds familiar to anyone. Thanks!

Sounds like you'll need to tighten your expansion valve, which is on the left side of the machine, attached to the plumbing manifold. It should be set so that after pulling a shot, the pressure on the pump gauge increases to roughly 12 bar.

What are you seeing for a rebound pressure now?

Cheers!

- Jake

Jake_G wrote:It should be set so that after pulling a shot, the pressure on the pump gauge increases to roughly 12 bar. What are you seeing for a rebound pressure now?

Thanks Jake! Not sure what rebound pressure is but while pulling a shot the pressure gauge goes to 12 immediately; when the shot ends it falls back to 3 and then slowly back to 2.

I should also note that the machine seems to just have a harder time getting through. I have to grind considerably coarser to get the same flow rate that I did earlier.

Does all that seem inline with your suggestion?

Are you plumbed?

12 bar is too high to be pulling shots. You should adjust your brew pressure to 9 bar or so and then assess.

motac wrote:when the shot ends it falls back to 3 and then slowly back to 2.

So your idle pressure is 2 bar? After you pull a shot, the brew pressure should briefly fall to something less than the brewing pressure (the exact number is unimportant), and then it should rise up to whatever pressure your expansion valve is set to. LM recommends setting it to 12 bar, but in reality it can be set anywhere between whatever your brew pressure is and 12 bar - no higher than 12, no lower than your desired brew pressure, lest it vent into the drain box whilst pulling a shot.

Can you see where the water is entering the drain box when you pull a shot?

motac wrote:
1. while pulling a shot the pressure gauge goes to 12 immediately; when the shot ends it falls back to 3 and then slowly back to 2.

2. I should also note that the machine seems to just have a harder time getting through. I have to grind considerably coarser to get the same flow rate that I did earlier.

The two symptoms you describe would be typical of 1 problem. The pump is putting out 12 bar or more.

1. It should go to 9 ish bar immediately not 12 (it might rise to 12 after a while if you have a choker, but that's a different thing)

2. having to grind coarser is common, as when 12 bar hits a finely ground puck it's much more likely to compress and slow the flow right down, compared to using a lower pressure.

I would recommend first using your blind filter, remove one of the heating element wires to the brew boiler if you can (it's probably tricky), so it can't fire up and affect results (water expansion on heating). If you try with the machine cold (the water still expands), the other way would be to fill the portafilter as full as you can with water when you lock it in to limit the water coming out of the boiler and the expansion...doesn't work that well though.

Then adjust the balanced bypass on your rotary pump to show 9 bar....which will fix the problem (unless the bypass has gone faulty).

Usually this sort of thing happens when people plumb the machine in without a pressure regulator....the balanced bypass doesn't normally go out adjustment without a reason. However, increased pump pressure is almost certainly the problem.

P.S. the reason pressure goes to 12 bar without the portafilter in, is because the pumps flow rate is higher than the Gicleur can pass...thinking about it, you could quickly adjust the pump pressure like that without the portafilter in...which would eliminate the water expansion on heating issue.

Hey all, thanks for your valuable input!

@Jake_G N
- Not plumbed in (yet .
- It doesn't rise back up to 12 but lingers around 2.
- The water properly drains in the tray, it seems like the pump is generating too much pressure and the system is dealing with that by siphoning off the surplus in the drain tray.

@DaveC I think you're on the money! The pump shouldn't go to 12 during a shot in the first place. A mechanic I spoke said it's quite likely the pump is blocked or chocked, making it overpressure when pulling a shot, and underpressure when idle. Going to confirm by bringing the machine in.

Again, thanks a lot, I'm learning something new every day here

motac wrote:A mechanic I spoke said it's quite likely the pump is blocked or chocked, making it overpressure when pulling a shot, and underpressure when idle. Going to confirm by bringing the machine in.

That's not the way these pumps work...
I asked if you were plumbed in because a typical mains pressure is 3 bar, and your pump will add the brew pressure setting (typically 9 bar) to whatever supply pressure is feeding the pump. There is no need to take the machine in for service unless you are unable to adjust the brew pressure yourself. The pump is not in the easiest location to adjust the pressure, but it can be done with a long and thin flat blade screwdriver.

The pressure adjustment is shown in the La Marzocco Linea Micra Espresso Machine Review, albeit with the outer case removed:

As Dave mentioned, once the pump pressure is set correctly, your issues should disappear.

Cheers!

- Jake

Hey all!

Reporting back. Went to a mechanic who solved the problem. Pump pressure wasn't the issue: there was a bit of rust-ish stuff inside the pump fitting, jamming it down (main issue); and the expansion valve was clogged up with scale fragments (secondary issue). All is well again, shot pressure back to 9 bar, resting back to 12.

This, by the way, after only 3 months of use (daily, but there's only two coffee drinkers in our household). The shop folks were mildly surprised as well but supposedly this isn't unique - some cities have issues with water that can manifest as early as a few months in. I was told to boil water before using it... sigh.

Bit of a bummer; my E61 machine did fine on our water for decades (they told me that's because it has a brass boiler as opposed to the Micra's stainless steel boiler).

Anyway, I learned something this week!

motac wrote:Hey all!

Reporting back. Went to a mechanic who solved the problem. Pump pressure wasn't the issue: there was a bit of rust-ish stuff inside the pump fitting, jamming it down (main issue); and the expansion valve was clogged up with scale fragments (secondary issue).

And this after only 3 months of use (daily, but there's only two coffee drinkers in our household). The shop folks were mildly surprised as well but supposedly this isn't unique - some cities have issues with water that can manifest as early as a few months in. I was told to boil water before using it... sigh.

Bit of a bummer; my E61 machine did fine on our water for decades (they told me that's because it has a brass boiler as opposed to the Micra's stainless steel boiler).

Anyway, I learned something this week!

Or you can use bottled water until you figure something out.

Funny thing, they explicitly told me not to do this, as bottled water often has a variety of minerals and salts that are harmful. So I was like, "distilled water then?" and they were like "nonono, that takes all the taste away and having no minerals hampers the extraction"... WHICH IS IT? MAKE UP YOUR MINDS