Group pressure issue la marzocco PB

Hi legends,
I am having an issue on my 2 groups PB, when one of the groups in use with coffee, and the other group only pour water, the pressure on the group with coffee will drop to 6 bar.
I had tech to check, he think it is normal to have the bar pressure drop, because there isn’t anything to stop water pouring.
today I went to my friends cafe and test the bar on his FB80, his FB80 will drop as well, but within 0.3 bar.

any idea? is this normal? Thanks

That drop in pressure is certainly not normal, Angus. We have a 2 group PB in our cafe, and the drop with both groups activated is nominal on our machine, not even half a bar.

I have a few questions for clarification:

  1. What is the pressure drop when coffee is being brewed in both groupheads?
  2. What is the flow rate of water out of the groupheads? Run the group with a graduated cylinder or something else under it with the screen in for 30 seconds. PB should be 250 ml in 30 seconds.
  3. Are there any other factors that cause that drop? What happens when you pull just water through both groups?

Hi Jacob
First of all, thanks for reply me back, I had test the machine this morning

  1. The pressure drop around 0.1~0.2 when the both have coffee in there
  2. This is one of my concern as well, when only have one group pouring water, it is normal, 250ml in 30 sec, but when both groups on, it only 180ml in 30sec
  3. I have done a few test, when the machine is off the bar pressure is 6, when it on it is 11, when only one group pouring water it’s shows 9 on the machine bar gauge, when both group pouring water it only 3 bar. In case of blockage in the filter, I had bypass the filter by connect the water source direct to the machine, but still the same, I had increase the bar pressure on the pump, but only increase the bar pressure for pouring, and still drop a lot. I had the boiler descaled twice as well to in case if any blockage in the pipe and boiler, but still no luck…

Sorry for my bad English, that’s just not my mother language, but hope I had made this clear enough

Hey Angus, great to hear back from you. Thanks for answering so thoroughly, you were very easy to understand, no need to apologize!

So, from what you’ve told me, I would personally take my attention off the water and focus on electric issues or other components. If your water flow is 250 ml in 30 seconds on both sides independently, that still means you aren’t seeing any restriction in water flow.

As long as you can fill a gallon jug in 30 seconds or fill a 5 gallon bucket in 2.5 minutes (2 gallons a minute water flow) through your filter we can rule out the blocked filter- you should definitely not run the machine without water filtration for any length of time if you can help it!

On to the next thought- if they can push the proper water amount through independently, but can’t together- that means that there isn’t sufficient pressure being created WITHIN the machine to keep both groups going at 9 bars.

There are a few parts that can cause this, but my first thoughts would be to check on your incoming power- make sure your voltage isn’t low…

Then check out the pump. The thing that fails the quickest and is the easiest thing to replace is the capacitor, which is responsible for beginning and sustaining that 9 bars of pressure.

That’d be my next move if I were you. Now I have a question about the test that you said you did:

Did you mean that when you switched the machine off it rested at 6 bars? Or when the pump wasn’t engaged? If you meant that the whole machine was off, the spike in pressure is just the machine bringing your boiler back up to temperature.

Let me know if what I have told you gets you any results. The pump is what I’m suspicious of, though there are other parts that could be malfunctioning that could cause your machine to go under pressure!

Make sure whoever you hire as a tech really goes through the whole investigation process, whoever you brought before didn’t give you an informed answer for your problem.

Hope this helps,


Thanks Jacoby
I bought this machine secondhand from the coffee machine service center, and setup myself in my garage without tech but electrician, what’s he have done is change my fuse in the garage to 20amps , check the main switch and change the power outlet, because this is just a temporary setup in my house before my cafe open, I didn’t install the water regulator, and I only ask the tech to come once, just in case it is because my setup, which he believe, there wasn’t any issue.

And yes I mean when the machine is totally switch off, the bar on the gauge is 6 bars. The reason I mentioned this is because I had call la marzocco Australia, he said it should be sitting in between 3~6 bars when it off.

I had test the water flow I can fill a gallon jug in 25 seconds through my filter.

Can you tell me where is the capacitor? Is it located in the box attached to the pump? I may ask the tech who sold me the machine to check that as well, or I am going to change it myself :smirk:

Nice! Good idea, making sure the machine works before installing in your

Do you have a multi meter? I would check at your outlet to make sure you’re
drawing 220-240v, your garage may have low voltage- which could be the
source of your issue.

The capacitor for the pump looks like a big silver battery that is attached
to the pump. I think capacitance is what you check for through a
multimeter, you should probably have a tech do that- because if I remember
correctly I thinks it’s possible to accidentally discharge the capacitor.

I feel like the voltage or the pump are probably your culprit! Let me know
what happens :slight_smile:


Thanks Jacoby
I will let the tech to do the job, just in case I kill it, will let you know what’s happening when I have fix that!:grin:

Hi Jacoby,
After discuss with you, I pretty much understand the problem might be the water supply is weak from the pump to machine, so this morning I went back and check this area, guess what? I FIXED IT! It is a really simple fix and you are definitely show me the right direction! The kinked hose! Yes it is, I accidentally put the drain hose on top of the supply hose.
Thank you so much for helping me, I am really happy with the results, as the problem has been 5 month!


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Hey!! There ya go!! So glad it was such an easy fix. I’m definitely going to keep this situation in mind if my wholesale customers ever have a similar issue! Enjoy your espresso machine! :grin:

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