Background: I purchased my La Marzocco GS/3 AV in 2009. It was manufactured in 2008, and was one of the infamous "fire sale" machines that had a string of problems believed to be caused by disruption when LM moved its factory that year and/or improper storage by the U.S. distributor. Unbeknownst to me, the steam boiler seals were defective from the start, leaking very, very slowly, and only when the machine was cold. The seals gradually got worse, leaking water into the brain box and contaminating the logic board, causing strange symptoms that would come and go. After a long vacation during which the machine was turned off, the seals leaked enough water to destroy the logic board. Back in 2014, I posted a report with photos showing how I replaced the steam boiler seals in 2011 -- a three year delay between doing the job and posting the report .

I still have the machine and use it every day. No leaks from the steam boiler seals have occurred since replacing them 10 years ago.

At the end of last month, after being away for 6 days between Christmas and New Years, I found water under the machine, mostly under the left front and middle rear of the chassis. I found a film of dried mineral deposits in the vicinity of the coffee boiler, but it wasn't immediately clear whether the coffee boiler heater seal was leaking or if it was the nearby flow control mod components I installed a couple years ago: a 3-way bypass valve in front of the heater plate and a needle valve ("Jake valve") a few inches away.

First thing I found was that the water under the middle rear of the machine was leaking from the drain box hose where it entered a hole in the countertop on its way to the sewer pipe. Evidently, the plastic had weakened and failed after 12 years of the hose rubbing against the edge of the hole when I moved the machine for maintenance. Easy enough to fix once I had a replacement hose in hand. In the meantime, I stuffed some paper towels against the hose to catch the water.

However, on some days I still found water under the left front side of the machine after warmup. But there was no sign of an active leak inside when the machine was warm. Finally, when the machine was cold, I caught the coffee boiler leak in the act. It was a slow but steady leak from the bottom of the triangular plate, with a drop of water oozing out every couple of minutes or so. I immediately ordered a replacement seal and some spares in case the steam boiler seals are close to failure as well. This thought was based on a mistaken recollection that I had also replaced the coffee boiler heater seal when I replaced the steam boiler seals 10 years ago. After reviewing my post above, however, I realized that I never replaced the coffee boiler heater seal. It was still the OEM seal installed at the La Marzocco factory over 12 years ago. Evidently, whatever error they made with the steam boiler seals (improper installation or wrong material) didn't happen with the coffee boiler seal, or the somewhat higher average heat of the steam boiler caused much faster deterioration of the OEM seals.

When the new seals arrived, I saw that they're not the same material as the OEM seals or the seals I used to replace the steam boiler OEM seals. The new seals are green, while the OEM and old replacement seals are black. The description in the GS/3 parts catalog is O-RING 3,53X37,69 FKM 70 SH GREEN. I have no idea what material any of these seals are made of, but presumably LM believes that the green seal material is superior to the black seal material.

Normally, replacing the steam boiler heater seal is relatively straightforward. But in my case, the bypass valve I use for flow control is in the way:



Luckily, the flexible plastic hoses made it a simple matter to remove the two mounting screws and lift the valve out of the way. I didn't have to disconnect the hoses, which usually requires re-cutting the ends and sometimes replacing the connector. I was able to carefully move and work around the thin steam pressure gauge tube, so I didn't have to remove it.

Here's what I found when I removed the coffee boiler heater:



Though well-oxidized, the copper heater tube appears to be in remarkably good shape for a 12+ year old machine, and the seal doesn't look too bad. However, you can see some mineral deposits around the inner circumference of the seal. Here's a closer look, showing some green "verdigris" on the heater element and more of that reddish-white stuff around the seal:



Looking closer still, the failed portion of the seal is clearly evident:



The is exactly the location where I saw the drops of water emerging from under the triangular plate. It looks like the reddish-white stuff may have gotten under the seal and dislodged or deformed it. Or, the material simply failed in that spot. Anyone have an opinion?

Here's a look at the seal after removing it from the heater element:



Note the rough, frayed edges in some spots, which look like the material has "oozed". I don't know if this is a normal result of the seal being squeezed during installation, or a result of the reddish-white stuff working its way under and/or around the seal.

It wasn't easy to get a good photo, but here's a shot of what I found inside the coffee boiler:



Before I get into the yucky stuff inside the boiler, note that the reddish-white stuff has migrated between the seal and seat at about 7 o'clock, where the leak occurred. It hasn't grown all the way to the end of the seat, but looks like it has built up enough to dislodge the seal.

As you can see, the floor of the coffee boiler is littered with green and white shards of mineral that appear to have sloughed off the heater element. I pulled some of them out and found that they were quite brittle. I'm amazed that none of this debris found its way into the tiny gicleur in the group head or the small fill port when draining the boiler.

I used a powerful shop vac to suck the remaining water out of the coffee boiler, which pulled out some but not all of the debris, then duct taped a 3/4" silicone tube to the shop vac hose and gave the inside of the boiler a good vacuuming. Then I used several rounds of damp and dry paper towels to grab the last of the debris, and finished with another vacuuming. Once everything was back together, I flushed the boiler twice before the final fill.

Next, I cleaned the heater element. I started by soaking it in full-strength distilled vinegar:



After accidentally knocking the glass over, I retreated to wrapping the element in the paper towels I used to soak up the spilled vinegar. That did a very good job dissolving the green verdigris and black oxidation enough so that I could remove them with a Scotch-Brite pad. I had to use a utility knife and some sandpaper to remove the last of the reddish-white stuff around the seal seat, taking care not to nick or scratch the metal seat, which could compromise the seal. Here's the result, with the new seal in place:



I also used a Scotch-Brite pad to removed all the buildup around the seal seat on the boiler, which you can see in the photo above of the gunk in the boiler. I stuffed paper towels in the opening to catch any bits of mineral and Scotch-Brite pad that flaked off, then gave the boiler one last wipe-out and vacuuming.

Over the years, a number of people have asked whether the seals should be lubricated before installation. I believe Chris Coffee techs told me they don't use lube. I remember using some back when I replaced the steam boiler seals, and our member/moderator Jake_G told me that he used a spray lubricant. I decided to use a thin coat of Molykote 111, which I believe is the lubricant generally recommended by La Marzocco. There have been some posts suggesting that Molykote isn't food-safe, but even if it isn't I'm not concerned about the tiny amount I used. I'm sure I've ingested a lot worse.

I couldn't find a torque spec for the nuts that secure the triangular plates. I asked Jake_G what torque he used, and he told me that he had calculated 17 ft lbs based on the size of the nuts and studs, and the materials. That's what I used. I started by screwing the nuts on by hand until finger tight, alternating nuts every turn or two in order to evenly seat the plate. Then I used the torque wrench to alternately turn the nuts 1/4-1/2 turn each, until the wrench clicked. I also used 17 ft lbs for the lock nuts.

It's possible to get the torque close without a torque wrench, but it requires some practice. Back when I replaced the steam boiler seals, I tightened the nuts using a method I picked up from an auto mechanic: slowly turn the wrench with minimal force until you feel it getting a little harder to turn. Then continue slowly and with only minimal force and "feeling the wrench". There will be a sudden increase in resistance when the nut seats against the work. If you go more than 1/4 turn after that, it's likely you'll strip the nut or screw. I often tighten screws and nuts this way, holding the wrench as lightly as I can but making sure the nut or screw can't turn anymore.

That's it. The new seal seems to be holding well -- no leaks -- and hopefully it will stay that way for at least another 12+ years. I'll be keeping a close eye on the steam boiler seals in case they're nearing end of life as well. If I'm feeling ambitious, I'll replace them proactively at some point.

Nice writeup. So what did the inside of the coffee boiler look like after you cleaned it? Was is nice and clean in there like something you want to drink water out of or do boilers really not stay so pristine? I have a gs3 on order currently, soaking up whatever I find on them.

Sorry, I should have taken a photo of the inside of the boiler after I cleaned it out. It was essentially pristine, probably not much different than the day it was made. There was still a tad of green scale around the input port at the far end the boiler, but I wasn't able to get to it. Better to remove it at the other end, but that involves removing and reinstalling the T-connector, which I believe uses some sort of thread seal. Not an easy task.

Here's a photo taken 10 years ago of the inside of my steam boiler when I replaced the seals. The machine was only two years old and the inside of the steam boiler was pristine, similar in appearance to the outside of the boiler.



The inside surface of the coffee boiler isn't quite as uniform in color, but that might just be a difference in lighting. It's just as smooth. Maybe a little discoloration in a few places. Again, not too different from the exterior. Being made of stainless steel, I wouldn't expect much change, especially since I use a cation softener that removes 100% of the water hardness.

I have no qualms about drinking water from the coffee boiler, now that the large mineral deposits are gone. I don't think the mineral deposits are a danger to health. They're mostly made from the contents of the water I drink from our tap. There could be some copper oxide from the heater element mixed in, but we all drink water from copper pipes.

Wow. That's an amazing endeavor. You have way more courage and ability than me. I also have a GS3 from 2008, but I think (not sure) mine may have been made prior to the fire sale. It was made in January 2008, SN 0312. When was yours made? As for leaks, I had one (don't recall exactly where the leak was) a few years ago, and had the machine "overhauled" by the tech department of a local coffee roaster/chain of coffee shops (shops use La Marzocco machines). So far, I've not had additional issues. Thanks again for your great write up, and please let me know when yours was made/sn, etc. Thanks!!! Dave

I have no faith in the Green seals after we had a similar leak in our brew boiler that leaked slightly when cold. I replaced it with a teflon seal that I feel is far superior.

Was not a teflon seal for your element available? Might that not be a better choice?

The green O-rings replaced black O-rings that, in the case of my steam boiler, leaked from day one. I doubt that LM would have changed the material to an inferior one.

The photo might be misleading, but it looks like your Teflon seal is solid. That wouldn't work with the GS/3 boilers. The inner seat face is chamfered (about a 45-degree angle), so only the edge of the Teflon seal would make contact with it. The O-ring has to be flexible. In my photos you can see the chamfered surface and how the O-ring re-forms to seal it.

Also, the sealing mechanism is completely different. The GS/3 heater plate is held against the boiler with three screws. Yours screws in. I suspect that the flexible O-ring could be abraded by the screwing motion, especially if overtightened, no lubed, etc.

The Teflon seal is solid.

Your explanation makes total sense!

Thanks for responding.

BaristaBoy E61 wrote: Thanks for responding.

Anything for a fellow CW afficionado!

Great post, thank you!

As someone who'd gotten used to replacing elements every two to three years on my old Vetrano, the condition of that 12 yr old element is astounding. Kudos to you and your good water chemistry!
My GS3 is less than a year old so hoping not to need this info too soon, and am trying to reform. I've become appropriately more diligent re conditioning what goes in.

Chris