Greetings, fellow Baristas. I have been a happy owner of my GS/3 for about six months now pouring succulent shots daily for myself, my wife and friends as I wake up and whenever I feel the urge. Serial is 0245 from 2007. Machine has never been cleaned thoroughly to my knowledge (I'm the second owner) - I think it was descaled here and then. I inherited the machine from the previous home owner who left me the machine and the Mazzer grinder with the house. I cleaned the grinder thoroughly. I did not take care for the GS/3 except backflsuh it with standard scaling solution with a blind cap. I knew things would fall apart soon given the complexity of this beautiful monster. Then sure enough I had the classic o-ring leak on the boiler left side (small puddle under the machine) which I fixed (both sides of the boiler were fixed with parts from the wonderful folks at La Marzocco). I attacked the vacuum breaker upgrade at the same time (thank you Peppersass - I followed the instructions to the tee) and all this was 3 weeks ago. It worked like a charm. Thought I was all good to go until machine has now sprung a new leak yesterday this time from the drainbox and the vacuum breaker.

I think it has to do with the cleaning. I upset the scaling pathways that were created between 2007 and 2015 with cleaning the steam boiler so some clunks of scaling residue may have loosened and clogging the system down the line.

Here's my setup: plumbed for water not the drain, Everprue H300 FIlter, machine starts at 7:00 am, turns off 9:30 am, I reaplced Steam Boiler O-rings and upgraded Vacuum Breaker successfully about 3 weeks ago. After the upgrade, steam would flow into the drain box and no hissing etc. no large amount of water upon cool down. The machine ran fine until yesterday when I experienced these symptoms:

1. Woke up after the machine had started and I saw an overfilled drain box with a little puddle of clear water under the machine - not a massive leak thank heavens. It looks like it happened on startup or cool down.
2. I cleaned up the water and waited for the machine to cool down.
3. After cooling I noticed the water leak is constant into the drain box and it is coming from the steam boiler OPV just left of the expansion valve. Important to note it is the OPV (Over Pressure Valve for the newbies) vacuum breaker - I checked this by opening the right side of the machine where I placed a T-junction for the steam boiler tube from the vacuum breaker which connects to the tube coming from the Steam Boiler OPV. I used a T-fitting to attach the Vacuum breaker tube to the drain tube coming off the steam boiler OPV.
4. Leak is constant and every 60 seconds or so - it sputters some water into the drain box - it is coming from the steam boiler which means the boiler is way overfilled because when I turn the water supply off, the slow regular leak stops!

What is causing the boiler to overfill then slowly leak? 8 choices is scary! Help.
1. One way valve in the line between the hot water mix valve and the steam boiler (A2chromepeacock fix below)
2. Brain box malfunction (I doubt it because when I sprung the o-ring leak there was no water intrusion)
3. Boiler probe malfunction (I could have messed the probe when re-inserting the wand on the o-ring fix)
4. Malfunctioning brand new factory vacuum breaker (probably not, it's brand new)
5. Filtered water causing the probe to ignore the water (boiler has been filling fine for 3 weeks after vacuum breaker and o-ring fix)
6. Scaling residue from my cleanup clogging something down the line (maybe the one way valve is jammed #1)
7. Malfunctioning Steam Boiler OPV?
8. Malfunctioning Expansion valve? (I have never been able to figure out how to get it not to exceed 12 bar without a drip - loosen it tighten it - it seems loosening or tightening has no effect on pressure gauge after all the lights go on).

I am stumped yet glad I found the source (I think). It is not leaking from the o-rings in the group. I think it is the one way valve in the line between the hot water mix valve and the steam boiler that is not sealing properly as mentioned by yellow_speedster and A2chromepeacock below:

A2chromepeacock: La Marzocco GS3 massive water leak through OPV (La Marzocco GS3 massive water leak through OPV [resolved])
Matt (mjbelcher): More than La Marzocco GS3 Refill Tank Malfunction (UPDATE - More than La Marzocco GS3 Refill Tank Malfunction)
Peppersass: Updating the La Marzocco GS/3 vacuum breaker (La Marzocco GS3 massive water leak through OPV [resolved])

Thanks to Peppersass, A2chromepeacock and Matt for helping me get so far. Before I proceed, I thought I'd post and check in with this wonderful forum and you the experts. I have half a mind to dump this machine but I think it needs some TLC and I'm back to normal. Help me get there please.

Peace by the ocean here in Santa Cruz. Blessed.

There are some confusing statements in your report that need to be cleared up before we can diagnose the problem:

1. Does water continue to leak into the drain box every 60 seconds even when the machine is turned off?

2. You say, "Important to note it is the OPV (Over Pressure Valve for the newbies) vacuum breaker". As you know, the steam boiler OPV and vacuum breaker are two different things. Did you mean to say, "and not the vacuum breaker"? Please confirm where the water is coming from. Sometimes it's hard to tell because water can fill both tubes (the one coming from the OPV and the one coming from the vacuum breaker) via the T-adapter.

Need the answers to the above questions, but it does sound like a boiler overfill problem. I don't believe it has anything to do with the expansion valve if the leak is coming from the fitting that's connected to the OPV and vacuum breaker. Also, I believe if the problem is a bad check valve in the mixing block the water would back up into the coffee boiler and you would see it coming out the expansion valve, not the OPV/breaker fitting. That's because water doesn't flow into the steam boiler unless the steam boiler solenoid is open.

It could be that a piece of scale has jammed the solenoid open. That could explain why the leak is slow and would explain why it still leaks when the machine is off (if, in fact, it does.) Shouldn't be hard to fix that one -- just need turn off the water, let the machine cool and get the steam boiler fill solenoid out for a cleaning.

A larger issue is the scale problem. It sounds to me like you're shooting in the dark because you don't know the mineral content of your water. You need to know that before you de-scale or use any kind of softener. Get a good water testing kit.

It's possible that your machine needs a major descaling to get rid of any scale particles that could jam things up. But I wouldn't do that without some advice from experts. But descaling can be risky for a couple of reasons: 1) particles can break loose and jam the works, and 2) if you don't get the descaling solution completely out of the machine it can cause corrosion. I have never descaled my machine in the five years I've owned it, and we have very hard water. I used a cation softener from day one.

You should not backflush with a descaling solution. You should only use detergent designed for espresso machines.

Peppersass thank you for your questions and insight. Here are responses to your excellent questions:

1. Yes, water continues to leak into the drain box every 60 seconds even when the machine is turned off and cool. Confirmed. When I turn off the water the slow leak stops. I did this overnight last night.
2. The water is coming from the Vacuum breaker. You are right. It is hard to tell but I disconnected the T and traced the water which is indeed slowly dripping from the vacuum breaker. The tube is full of water all the time.
3. I have not back-flushed with a descaling solution. I only use detergent (1/4 tsp) which is designed for espresso machines.

Looking forward to hearing the diagnosis. After I posted yesterday, I cooled the machine, drained the steam boiler using the ball valve. Checked the connectors to the probe - all seemed working. Got a "T.ProbeUnconnect" message which eventually disappeared after in/off sequence. I think there is a jam somewhere.

One additional symptom which bothers me and maybe related is the steam boiler pressure gauge. When you engage the steam wand on the left, the gauge on the left rocks back and forth like it is dancing by about 0.2 - 0.3 bars almost and there seems to be a fair amount of vibration - the steam pressure does not seem smooth but very agitated at 1.5 bar. Don't get me wrong it is amazingly powerful but just feels a little like something could explode! it's not smooth like it used to be. It was smooth only upon first operation after draining and refill. Now things are back to normal: slow leak upon cool-down from vacuum breaker. Should I separate the two tubes from the T-junction?

Thank you for helping me.

More questions:

1. After disconnecting the tubes from the T-adapter, have you verified that no water is coming from the steam boiler OPV?

2. When you drained the steam boiler and turned the machine back on, after which I assume the steam boiler filled and came up to temperature, did you get steam when you turned on the steam wand or did water come out after the normal wand purge?

3. Are you absolutely sure no water is flowing from the coffee boiler expansion valve except when pulling a shot or immediately after when the pressure increases due to the heater coming on?

I asked question #1 because typically the water pressure from an overfilled steam boiler causes the vacuum breaker valve to close. You would probably see some leakage before that happens, then it would stop. After that, I would expect the OPV to trip and water would flow out of that tube. After the pressure subsides, the vacuum breaker will open again and the cycle would repeat. That sounds a lot like your symptoms, but my theory depends on the OPV relieving the pressure. If it was just leaking from the vacuum breaker, you would expect a steady stream, not leakage every 60 seconds. A cycle of pressure being built up and then released by the OPV makes more sense. Also note that water can travel from the OPV tube to the vacuum breaker tube and back up into the breaker.

I asked question #2 because you spoke about the steam being amazingly powerful, it sounded like the machine is capable of normal steaming. I wouldn't expect that to be the case if the steam boiler is overfilling. There's no room for steam when that happens and you should get mostly hot water from the wand.

I asked question #3 because earlier you mentioned that you've been having trouble adjusting the expansion valve. If you've adjusted that valve so that it opens at or near line pressure, then you could get a continuous or intermittent flow into the drain box, even when the machine is off. I don't believe this is happening, but it would be good to rule it out. If this isn't the problem, we can discuss adjusting or replacing the expansion valve after the main problem is resolved.

I believe the action of the steam boiler pressure gauge is consistent with the steam boiler overfilling -- i.e., the pressure is fluctuating up and down as you draw steam (or water) off the boiler but it continues to fill. I vaguely recall seeing the gauge do weird things when my steam boiler overfilled.

I'm concerned about the "T.ProbeUnconnect" message. That means the CPU isn't getting a reading from one or both of the boiler temperature probes. I've only seen that when the logic board has been contaminated by a water leak. If it happens again, shut off AC power to the machine immediately. Note that steam boiler overfill is also a common symptom of logic board water contamination.

I still think the most likely cause of the steam boiler overfill is scale lodged in the steam boiler autofill solenoid valve. That would explain why the leak continues when the machine is turned off. The only way water can get into the steam boiler is through the autofill solenoid valve. I don't see any other path, such as a stuck check valve, whereby water can get into the steam boiler. If that's wrong, I hope other readers will correct me.

Thank you for your attention. Answers below.

1. After disconnecting the tubes from the T-adapter, have you verified that no water is coming from the steam boiler OPV? >>In progress.

2. When you drained the steam boiler and turned the machine back on, after which I assume the steam boiler filled and came up to temperature, did you get steam when you turned on the steam wand or did water come out after the normal wand purge? >>I did not check. Come to think of it I think it is spurting water not steam!! I never checked. And I never purge water from the steam wand! Except today when the machine cooled I noticed no leak in the drain box. I said to my self, "Strange, maybe the problem is fixed." Then I noticed the steam boiler pressure gauge: it was at max. The machine is off/cooling 3 hours now. So what do I do? I engage the steam wand handle and voila, a few drops of water spurt out and the gauge jumps down to zero and the leaking from the OPV (still checking if it's boiler OPV or vacuum breaker) restarted. Every minute. I have a video of the constant leaking. How can i post a video?

3. I am quite certain the only time water exits the expansion valve is upon warm up and after shot are pulled.

Your comments are very revealing particularly how you point out that water can travel from the OPV tube to the vacuum breaker tube and back up into the breaker. I am checking this now by separating the tubes because I cannot tell for sure of what is happening there.

I have never seen the "T.ProbeUnconnect" message until now and i know what caused it. I disconnected it and reconnected the wire. And this was the machine telling me it happened and not the logic board. So here's what went down: i opened it and reconnected the wire connector to be sure I had screwed it in tight. When I drained and refilled the boiler I saw the message and I could not get rid of the message on warm up. So I thought it will go away once all the blue lights come up. Did not happen. So I took a guess and turned the machine off and then hit the power button on the back. Upon re-powering on again it was gone and I trsut i will never see it again until I manually disconnect the wire again.

So my action items:
1. Check where the leak is coking from after separating the tubes: OPV from steam boiler or vacuum breaker valve.
2. Drain and refill boiler and turn steam wand on to observe whether water or steam are exiting and what ratio.

Why is the overfill occurring? Is the probe not sensing filtered water? Pending water testing, should I change the Temp Probe setting from Low to Medium? I think i will wait until above issues are identified.

Please point me to a diagram /pic of location of 'steam boiler autofill solenoid valve". Is this the one way check valve?

I thank you for your patience and helping.

rajivsab wrote:Why is the overfill occurring? Is the probe not sensing filtered water? Pending water testing, should I change the Temp Probe setting from Low to Medium? I think i will wait until above issues are identified.

Please point me to a diagram /pic of location of 'steam boiler autofill solenoid valve". Is this the one way check valve?

No. It's an electically-triggered valve. When AC is applied to the solenoid by the CPU, the valve opens and water flows into the steam boiler. When AC is removed, the valve closes. That should prevent any water from entering the steam boiler. If a piece of scale or debris is lodged in the valve, it may not be closing all the way.

The valve is labeled as (I) in the first photo in the document accessed via this URL:

/downloads/ ... aulics.pdf

These flow diagrams, posted by erics, are very helpful for diagnosing issues like yours.

I don't believe the overfill is being caused by the level probe sensitivity being set too high. The level probe only comes into play when the machine is on and the CPU senses that the steam boiler level is low. Then it opens the solenoid valve referred to above and turns on the pump. If there was a problem with probe sensitivity, you would hear the pump running continuously. But if the steam boiler is being overfilled when power is off, then I believe it can only be a problem with the solenoid valve.

Hello. I separated the tubes and writing to confirm the leak is indeed emanating from the Vacuum Breaker teflon tube. After separating the tubes, I counted 26 drops per 60 seconds so one drop every two seconds is streaming out of the tube. No water is coming out of the Steam Boiler OPV tube. I think the air pocket in the tee junction made it appear that there was a leak every minute. Next I am going to reconnect the teflon tubes, drain and refill the steam boiler and observe water/steam behavior from the steam wand upon power up to confirm your suspicion. Reading your followup above, if indeed a piece of scale or debris is lodged in the valve and it may not be closing all the way, should I directly go to opening up the solenoid valve and clean it thoroughly at the same time? Or is this a non-serviceable part and I need to replace? Thank you.

Here is a video of the leak before the teflon cables were separated showing the leak from the Vacuum Breaker.

[youtube]https://www.youtube.com/watch?v=cagZzyH ... e=youtu.be[/youtube]

More questions:

1. When the machine is off, what pressure do you see on the left (steam boiler) pressure gauge?

2. What is the line pressure going into the machine (i.e., to what pressure have you set the regulator, if you're using one)?

In normal operation, once the steam boiler starts to generate steam during warm up, it takes very little pressure to close the vacuum breaker. Normally, as the steam pressure builds, you hear a lot of sputtering at the breaker/OPV fitting in the drain box and see some water bubbling out. Then all of a sudden you'll hear a pop and it will stop. That's the sound of the vacuum breaker closing due to steam pressure from the boiler. I can't recall the exact pressure where the valve closes, but I think it's somewhere between 0 BAR and 1 BAR.

What's odd is that the vacuum breaker is passing water. If the boiler is overfilling at line pressure, water would flow into the valve but the water pressure should close the valve. The only way that wouldn't happen is if the water pressure is very low -- so low that it doesn't close the valve. That could happen with a very slow leak that's caused by the steam boiler autofill valve not closing all the way, either due to a piece of debris lodged in it or a mechanical failure like a worn out spring. The very slow drip from the vacuum breaker is consistent with that.

I've never removed or serviced my steam boiler autofill valve, but it doesn't look particularly difficult to get it out if you do it carefully. I don't know whether the valve can be serviced. Erics or someone else may be able to comment. Once you get the valve out, you can remove the coil, which is the black box. You just unscrew the nut with a wrench and the coil can be slipped off. Once the coil is removed, I would soak the brass part in vinegar. Hopefully, that will dissolve any obstruction. It looks like the valve can be disassembled, but I'd be really careful doing that. It's probably got a spring in it so you want to avoid parts flying out all over the place. You also want to make sure to note the position of each part for reassembly.

The cost of replacement is $163 from LM USA.

Before you proceed with any remedies, I think it would be a good idea to call LM USA. They have probably seen this before and can probably verify whether it's the autofill solenoid valve, and they can tell you whether the valve can be serviced.

Answers:
1. When the machine is off, what pressure do you see on the left (steam boiler) pressure gauge? When OFF and completely cool I think zero definitely less than 0.5. Today with the machine still hot two hours after shutdown, it was all the way at the top/MAX until I released the pressure with the steam wand and it shot down to zero ASAP where it currently stands now.
2. I don't know the answer to line pressure into machine or the regulator setting - I am not using a regulator. But interestingly my Everpure water filter did have a pressure reducer which I broke when i was replacing the filter - the filter head had a 1/2 GPM flow restrictor which broke which makes me wonder if this is what caused all my problems in the first place. As I recall, my O-rings sprung a leak a few months after I removed this flow restrictor.

In my case, upon startup, the steam pressure builds in about 10 minutes, then you hear some sputtering at the breaker/OPV fitting in the drain box and I see some water mostly steam bubbling out and then yes all of a sudden I hear a muffled pop and it stops. It's a very gentle pop since I did the vacuum breaker upgrade. So yes, the new vacuum breaker closes fine due to the steam pressure from the boiler and I think the exact pressure reading when the valve closes is less than 1 BAR. But your comments make me think that maybe if I went back and installed the flow restrictor that EVERPURE recommends this may help solve the problem. Do you think it's a scale particle compromising the system or water pressure? The slow regular leak does not occur when the machine is hot only when cool. And when cool the vacuum breaker is not shut close - is it? Now we have an added complexity to my problem it seems. Water pressure?

I don't know what to do next. I will call LM tomorrow for certain.

Thanks.