La Marzocco GS3 AV pump runs periodically at idle.

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by pavoni »

Hello all,

I have a GS3 AV from 2011 and have a new issue. I am not sure how to attach pictures but I will be using the images in the "La Marzocco GS3 Hydraulics" that I have seen in some of the threads here. My steam boiler pressure would max out (indicated 3 bar) if it sat idle for a 4+ hours. Using the tea button would drop it back to a normal 1.6 or so. Sometimes using the tea would cause a drip or two to come out the portafilter or the brewing solenoid drain (left side of drain pan). I ordered a valve and then when I went to replace it I discovered that there were several check valves on this machine... and this one has two between the mixing valve and steam boiler (J in the reference image).

The steam pressure seems to be constant at indicated 1.6 but the pump comes on briefly every 15 minutes or so. The steam boiler is making noises like it is "heating" or maybe it is a slow steam leak? I did notice that the drain tray under the brew solenoid drain is damp like it is weeping. Also the little squares one the display the one of the right blinks on briefly every 2 seconds and the one on the right goes 10-15 seconds before it goes on briefly. I don't detect any steam leaks but the steam boiler is constantly making noise like it does when it is heating.

I am beginning to wonder if after 10 years of being on almost 24/7 that that some of my other check valves may be bad? If I include the one on the pump I count 6 on my machine. 1 on the pump. 2 cold input to mix valve (A) 3,4 on tube from mix valve to steam boiler (J) 5 between solenoid and tube (H) to fill the steam boiler 6 is on the input of the volumetric flow sensor (C).

Is it possible that if the check valve at (H) doesn't work and the solenoid (I) leaks a bit that would allow water to go from the steam boiler to the causing it to weep? Or am I barking up the wrong tree and should be looking elsewhere? I have two more check valves on order and hopefully LM USA will ship them soon.

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pavoni (original poster)

#2: Post by pavoni (original poster) »

I should have included this in the original post but here is the image I was using when describing my issue above:

I found this image in a 2010 thread started by @A2chromepeacock here. It was a great help in how to get to the check valve between the mixing valve and pipe (J).

Here is a link to the PDF I was using: La-Marzocco-GS3-Hydraulics.pdf I found it did a great job of explaining the flows and helped me visualize how it was supposed to work as well as play "what if" things like solenoids or check valves were not functioning as intended.

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#3: Post by Peppersass »

I can't quite reconcile your symptoms. Some additional information might help:
  • Is the machine plumbed in or using the reservior?
  • Does the pressure rise gradually during the 4+ hour period, or does it happen quickly?
  • Does autofill come on every 15 minutes as the pressure is rising, or does this only happen after you release the pressure via the tea wand?
  • Have you made any changes to your water lately?
  • What's the mineral content of your water? Do you use a softener?
  • Are you using a carbon filter?
First, the O-rings in the check valves can and do wear out. My GS/3 AV is a little over 12 years old and I've changed the check valves twice. \It's also possible, and a lot less expensive, to replace the O-rings, but it takes some tools and skills (see Jake_G's post Replacing Seals on La Marzocco GS3). With a machine as old as yours, I'd replace all of the check valves or O-rings.

Second, note that LM added the second check valve in the path terminated at J to prevent boiler overfill if the check valve at the mixing valve fails. It's unlikely that both check valves would wear out at the same time, but if the water is contaminated with scale or debris they can certainly fail at the same time, causing an overfill.

Third, you're correct that failure of the check valve at H and the solenoid at I could cause an overfill. Again, it's unlikely that the valves would wear out at the same time, but they could be clogged at the same time by scale or debris in the water.

There are a number of possible causes of excessive pressure in the steam boiler: 1) overfilling due to faulty check valve and/or solenoid, 2) overfilling due to lack of minerals in the water, 3) overheating or overfilling due to faulty logic board (usually caused by water contamination from a leak), 4) overfilling due to faulty level probe/wiring, or 5) overheating due to faulty temperature sensor,

I don't think overheating is likely. It would probably cause the OPV (in can R in the photo) to open with a loud pop and steam would pour into the drain box. That's not happening, right?

The symptoms do seem consistent with a faulty check valve in the steam boiler autofill path, but as you point out the solenoid valve would have to be faulty, too. The O-rings in the check valves do eventually wear out, but it's less common -- but not impossible -- with solenoid valve plugs. However, both can be jammed open by scale or debris in the water. If your water is hard and you don't use a softener, that could be the problem. Or, if you water is hard and you do use a softener, then your softener isn't working. If you use a carbon filter, it might be breaking down, or if you replaced it recently it might not have been fully flushed. Little carbon particles can jam check valves and solenoid valves.

The dripping from the group and exhaust valve could also be explained by debris in the water that has contaminated the 3-way valve. But I don't see how leaks from those two sources would be triggered by using the tea water, unless the physical vibration from the tea water solenoid is dislodging a little water from the 3-way because it, too, is contaminated with debris. Doesn't seem likely, but it's possible.

I'm puzzled by the autofill coming on every 15 minutes, which is why I asked if that's happening when the pressure is building in the steam boiler or after you release the pressure by running tea water. It almost sounds like water is leaking out of the boiler, then it's being re-fiilled. This could happen if you're using the reservoir and the check valves in the J path are failing. In this case water goes in when autofill is called for, then leaks back out into the reservoir, then the cycle repeats. You would see the level in the reservoir going up and down (marking the reservoir with a piece of tape can confirm if this is happening. If you're plumbed in, I can't see why the autofill would be coming on every 15 minutes -- because water can't leak from the steam boiler against the line pressure.

Unless there's a leak. And if there's a leak, then the other behavior could be due to the logic board having been contaminated.

As a precaution, I would turn off the machine, unplug it, and remove the side and top covers to check for leaks inside. Water from leaks frequently finds its way into the brain box under the steam boiler and onto the logic board. Minerals in the water can cause shorts on the logic board that can wreak all sort of havoc. If you see don't see any signs of water or dried mineral deposits, you can proceed to troubleshoot other potential causes, though it's still possible the logic board has been contaminated (come back to that possibility after ruling out the other possible causes.)

If you do see water or mineral deposits inside the machine, or you rule out all other possible causes, remove the rear cover, pull out the brain box, remove its cover, and inspect the logic board for signs of water or mineral deposits. Best to disconnect the wires from the board and remove the board so you can inspect the underside and the box underneath the board. If you see any sign of water or minerals, clean and dry the brain box, then thoroughly dry the logic board and remove any deposits with 90% Isopropyl alcohol (IPA). Make sure it's completely dry before reinstalling.

Before using the machine, you must find the source of the leak. Check the boiler seals at both ends of each boiler for any signs of leakage or evidence of water/minerals having dripped down the sides. Check the steam boiler drain valve on the left of the machine. It's not a high-quality part and has been known to leak, especially if it was slightly unscrewed from the boiler the last time the brass cap was removed. Check all fittings and the areas immediately underneath them.

pavoni (original poster)

#4: Post by pavoni (original poster) »

I apologize for the length of this post but I am trying to fill in details that I should have included in my earlier posts.

Is the machine plumbed in or using the reservior?

The machine is plumbed in (both input and drain)

Does the pressure rise gradually during the 4+ hour period, or does it happen quickly?

It seemed to me that it stayed low for quite some time and then jumped up to 3 at the four+ hour mark. But in retrospect that might be an artifact of how I was observing the pressure. I would open the tea and/or steam and the pressure would drop. I would then keep checking it often after that and then slowly check it less and less often.

Does autofill come on every 15 minutes as the pressure is rising, or does this only happen after you release the pressure via the tea wand?

Sorry for the confusion. I think I had more than one issue going on and I did a poor job of describing it. I will try to do a better job below.

Have you made any changes to your water lately?

What's the mineral content of your water? Do you use a softener?

Are you using a carbon filter?

I will answer these three together. I have a well (since the 90's) and when I first got the GS3 I tested the water and it indicated that I didn't need to do anything. It is soft so I don't have a softener. When I first got the GS3 (2011) I installed a 2x10 filter with one carbon and one particulate filter for the machine. In 2019 my house was finished (same property) but I am now using a 4x20 whole house filter (carbon, and 2 particulate) but it is the same well.

My first sign that something was wrong was steam pressure was indicating 3 bar and the steam wand was water and very little steam. After 10-15 seconds of purging the steam wand it would include some steam but it also included quite a bit of water. I concluded that steam boiler was over full. I decided to remove the steam fill probe to inspect it. I unplugged the machine, let it cool and started to remove the probe. It started leaking (confirming over full steam boiler) and I re positioned the machine onto the right side to stop the leaking. I then removed the probe and found a small buildup at the very tip of the probe that I used a green scrubby and water to remove. I replaced the fill probe and powered on the machine and it was still over filling the steam boiler and the pressure was too high and the steam too wet.

So I ordered a check valve and when it arrived I ...I remembered the drain valve on the steam boiler... so I connected a drain hose and drained the steam boiler. I also drained the brew boiler by unscrewing the adjustable fitting (M). I had read that if the check valve(s) on pipe (J) fail the steam boiler can overfill. I also learned that my machine has six check valves if I include the one on the pump. I only ordered one valve (stupid) but when I removed the mixing valve as described in 2010 thread I refer to in post #2. This gave me easy access to three check valves and all of them flow in both directions. I soaked in vinegar, ran water, compressed air, and even poked them in hopes that I could knock something loose and make them functional. I decided that with only one valve I would replace the one between the mixing valve and pipe (J). I chose that one over the one in the middle of pipe (J) because I could replace the middle check valve later without removing the mixing valve.

I put everything back together and ordered two more check valves from LM USA. I then turned on the machine, filled the brew boiler (purging the air with the bold on the top of the brew head). I checked for drips while it was heating. After 4 hours the steam pressure was still at 1.6 (normal) and an additional eight hours later (over night) it was still at 1.6. Unfortunately it the pump would come on every 15 minutes. I scratch my head and post on HB. I think that there must be some slow leak somewhere but I don't hear an obvious steam leak and the inside and under the machine dry.

I get the wrenches out again and make sure that all the fittings that I have touched and all the ones on the steam boiler were snug. It was then I noticed a bit of residue near the fill probe. So I unplugged the machine and let it cool. This time when I removed the fill probe it didn't leak! (yay). I took the copper washer and cleaned it up with a green scrubby and reinstalled the fill probe. Once the machine was warm again the steam gauge is nominal at 1.6 bar. The pump still runs but is now a couple hours apart. The steam boiler is making a quiet noise just like the noise that that is made when the heating element is on but the noise doesn't quit when the element turns off. How often should the pump run to top things up?

Current status as of now... Still waiting for LM to ship me my check valves. The steam boiler seems to be making more noise than it should. For me to hear it I need to be in a quiet house and closer than about 10ft from the machine so it isn't loud. I have looked again to see if I could detect steam leaking from the vacuum breaker, safety release, etc. I also looked for water/drips but everything is dry. Except I notice that the drain that is connected to the solenoid on the brew head seems to weep a bit every few minutes. This is the same place that drains when you run the back flush.

Somewhat unrelated I took my old (failed) check valve and managed to remove the clip and tried to push the plunger out but was unable to. I didn't feel that I should use a hammer so I put the clip back in and would like to find a cross section of the check valve and/or instructions on how to service these valves.

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#5: Post by Peppersass »

Sounds like failure of the check valves at J caused of the steam boiler to over-fill. But since the new check valve appears to have solved the back flow problem at J, there's no way to know whether the second check valve has worn out or it was clogged with scale or debris that you cleaned out. In any case, given the age of your machine, I would replace all of the check valves. The latest model check valve LM uses is expensive, but it's supposed to require less frequent replacement.

It takes some force to punch out the check valve plunger. But that usually tears the O-ring, so the exercise is useless for diagnostics. It's only useful if you're going to replace the O-ring.

I'm a bit concerned about the weeping at the 3-way exhaust valve. That's got to be caused by either a worn out 3-way plug or debris in your water (or maybe a weakened 3-way spring, but I'm not sure about that.) I think you said it would occasionally weep from the group, too. Is that the case? This isn't a huge problem because the exhaust and group drain into your plumbed-in drain box, but if the 3-way has an issue it should be fixed.

Again, you can't yet rule out that scale or some sort of debris has gotten into your water.

It sounds like the level probe was leaking. That would explain why the pump was coming on every 15 minutes and the heater every 2 seconds, and why those two things stopped when you cleaned up the fitting. It might still be leaking a little, which could explain the noise you're hearing (i.e., it's steam escaping.) The autofill should only come on when the water level drops due to running tea water or steam. It's better that yours is coming on only every two hours instead of every 15 minutes, but it shouldn't come on at all if tea water or steam haven't been run. If it does, that could indicate a leak.

I had some issues with sealing the probe fitting. In older models, LM used a fiber gasket that deteriorated over time. My understanding is that they added a copper washer to make up for that (they kept the fiber washer, which fills an indentation in the probe fitting.) When my fiber gasket went, I used Teflon tape as a temporary fix until I could get a replacement gasket. I got the gasket but never changed it because the Teflon tape kept working. That was eight years ago! You can read more about it in my thread La Marzocco GS3 Level Prove Gasket.

When looking for steam leaks, I take use plastic tubing as a makeshift "stethoscope", putting one end to my ear and putting the other end close to each fitting on the boiler. If a fitting is leaking, the tubing will direct the sound to your ear. That's how I found the leak at the steam level probe. I use the same tubing that I use to drain the steam boiler. I think it's 3/4" OD.

Another thing concerns me: If the steam boiler probe has been leaking, then it would have leaked water when the boiler overfilled. You might want to check again for any signs of leakage around that side of the boiler. There are several holes in the chassis near the bottom of the boiler on that side that can allow water to drip on the brain box and get inside via the screw holes in the cover.

pavoni (original poster)

#6: Post by pavoni (original poster) »

@Peppersass thank you very much for the detailed replies.

In the process of replacing my single check valve I had three out of the machine. I would blew through them to confirm functionality (or in may case lack of function...) None of them worked. When I got the new model in hand I tried it and it held pressure when blowing the "wrong way". I ordered two more from LM US and hopefully they show up sometime this week. It sounds like I should get three more and just replace them all. You are right they are expensive at sixty something a pop. But it appears replacing them is long over due. Also if I have six bad ones laying around I might try to take to old model apart and source some new o-rings to keep as spares or at least a learning experience if I can't make them work.

It sounds like I should get a tube or an stethoscope like a car mechanic would use to see if I can narrow down where the steam/leak is coming from. But the inside and under the machine is dry. (the only water seems to end up in the drip tray)

My steam boiler level probe only had a copper washer (no fiber or anything else) between it and the wall of the boiler. But after reading your thread from 2013... it sounds like I need to get some teflon tape. Did you wrap them around the reducer threads and the smaller probe fitting or just the reducer? The picture of the probe I saw at espressoparts looked straight does the one from LM US come bent?

My current thought is if I replace the remaining check valves and then find the steam leak I should fix the pump running while idle problem.

That leaves the weeping from the three way valve on the group head. If I wipe the drip tray dry and go to bed the next morning I see dampness on the back wall of the tray but not enough water to get to the drain at the bottom center. Darn, was going to take a picture to show as it has been idling for 4-5 hours... but the darn thing has not leaked a drop in that time or if it did it evaporated and the drip tray is bone dry. I guess I need to pay closer attention to when it weeps and how it relates to back flushing, usage, etc. The group head has not been leaking for several days and I seem to be unable to make it do so. I doubt that it fixed itself but I have a hard time believing that a replaced check valve would fix it. Could coffee fines cause this if I don't do enough back flush cycles?

Leaking water or condensing steam scares me. My machine over filled the steam boiler the first week I had the machine (2011) and blew water all over the place including the brain.

Now to check for scale or grunge in the boiler(s). Is there an simple and easy way to check? I don't have a borescope but would this work to peek in? If so is there a recommendation for one that would work (bonus points if it is affordable)

My plan is to
1) find/fix slow leak (right now suspicious of fill probe)
2) replace remaining check valves
3) do step 1 again since fittings were unscrewed/screwed
4) work on the weeping and figure out the status of the boiler scale/crud buildup.

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#7: Post by Peppersass »

You're on the right track.

I wrapped the thick part of the probe fitting that screws into the steam boiler. I didn't have any leakage from the small threaded portion, but I suppose that's possible. I'd try to confirm the leak before wrapping, then if it's confirmed wrap the large fitting first and re-test. You don't have to drain the boiler to do this, just let it fully cool.

I think I replaced the probe at some some point and had to bend it, but my memory is vague on that. I wouldn't be surprised if the LM probe isn't pre-bent. It's not hard to bend the probe. Use the old probe as a guide, Lay it over a piece of dowel or similar rigid small diameter piece like a bolt held in a vice, thread rod, etc., and lay the new probe across the piece so the tip lines up with the tip of the old probe and gently bend, making sure to hold the new probe so the tip remains aligned with the old probe tip. (If anyone else has a better way to do it, please chime in!)

Now that I think of it, maybe when the steam boiler overfilled water slowly leaked out of the OPV instead of the level probe fitting, where the leak might be so small that an insignificant amount of water leaks out before the OPV triggers. That would explain why there's no water in the machine and why the autofill came on every 15 minutes. It might have been such a small amount of water coming out of the OPV that you might not have noticed. Now that you've replaced one of the check valves at J and cleaned up the level probe, you just have a small steam leak. Eventually -- in your case every two hours -- that'll cause the water level to drop and autofill to come on.

However, it's worth checking all fittings connected to the steam boiler and the fittings at the other end of the tubes, such as the one that connects to the steam valve, and make sure the steam valve isn't leaking -- it may need servicing, for which there's a rebuild kit.

If you haven't already, get a water hardness test kit to make sure there's no chance of scaling. I like the Hach hardness kit that Amazon sells, but the API test kit, which is a lot less expensive and also measures alkalinity, will do. Just not quite as accurate.

I would also carefully examine the output from your carbon filter to make sure there are no carbon particles coming out. We have sediment in our well water, which is removed by a whole-house filter, and when I change the filter I check for sediment in the output by running some water into a clear glass with a large bottom, letting the bubbles subside, and looking down into the glass while it sits on a light-colored background. You can do the same with the output from the carbon filter.