La Marzocco GS3 steam residue on panel

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
txrpls
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#1: Post by txrpls »

I just started noticing that my front panel was showing steam residue or fogging to the right of the portafilter. I though it was probably the safety valve, so I replaced it (machine about 3 years old). It did not relieve the symptoms. It turns out the water was coming from the line running from the vacuum breaker assembly on the steam boiler. I also noticed that it was dripping out of the expansion valve (every 1.3 seconds) and not out of the safety valve. I also noticed that the pressure was reading 12 bar, WTH? I do not check the pressure meter that often as I made the Strada modifications over a year ago and watch that meter on top of the group head.

I then decided to check the steam boiler probes after reading a post on here. No scaling, all clear. Put the machine back together and fired it up. Still the same problem. I reduced the pressure to 9 bar and the steam pressure to about 1.6 Bar. I still have dripping/fogging coming out of the steam boiler vacuum valve and an occasional drip out of the expansion valve. I think the steam boiler expansion valve may be defective.

What is puzzling is why the sudden jump in coffee boiler pressure? I had to adjust it quite a bit to get it to 9 bar. It had never been changed since the machine was delivered.

Is there some form of relationship between the coffee boiler and the steam boiler?

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Moxiechef
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#2: Post by Moxiechef »

I'm a touch confused as to where you're dripping is, you said "left of the portafilter", did you mean right? Left is the solenoid drain but right is the steam vacuum breaker drain and the expansion valve. My steam vacuum breaker has to be cleaned about every six months. It starts fogging up the front panel under the key pad. I've cleaned it twice and rebuilt it once. It gets a reddish/black crystalline buildup.

http://www.lamarzoccousa.com/wp-content ... 6COLOR.pdf

txrpls (original poster)
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#3: Post by txrpls (original poster) replying to Moxiechef »

Good catch. I meant the tube farthest to the left which is right the portafilter. I corrected the post. Just to be clear we are talking about the assembly listed as no. 14 on page 33 of parts catalog your link? if that is the case, what do you use to clean it?

Moxiechef
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#4: Post by Moxiechef replying to txrpls »

That's it. Just a soft nylon scrubby but I do have backups of all those parts. Mine started bubbling last week, I'll get to it next week but since I don't want down time, I'll check to be sure I have all the parts before I start in case I mess one up.

txrpls (original poster)
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#5: Post by txrpls (original poster) »

I'm going to order the entire assembly tomorrow. Any idea why the sudden jump in the coffee boiler pressure?

Moxiechef
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#6: Post by Moxiechef replying to txrpls »

No idea about the pressure jump.

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Peppersass
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#7: Post by Peppersass »

Definitely the vacuum breaker. Mineral deposits build up inside over time and it's normal to require service every 6-12 months. Sometimes it goes longer. Just serviced mine after what seemed like a very long time, somewhere in the 12-24 month range. That may be because I use a cation softener that removes all hardness. Recently I let the softener go too long without recharging and the hardness skyrocketed, which is probably why my vacuum breaker got fouled.

You don't need the entire assembly. You just need the moving parts inside, which are available as a rebuild kit from your dealer or LM USA at much lower cost. There are only three parts, which you can also buy individually: A shaft, an O-ring and a Teflon seat. Usually the only thing that really needs replacing is the O-ring, which gets hard and/or caked with mineral deposits. Buy a supply.

The shaft and seat can usually be cleaned off, but it's not a bad idea to buy a couple of each just in case. Probably a good idea to get a supply of copper washers, too. They're usually reusable, but good to have just in case. Used on a lot of fittings in the machine.

Here's a post that shows the disassembled vacuum breaker.

Here's a post on regular maintenance items, including links to LM's 6-month and 12-month checklists.

Not sure about the boiler pressure, but the increase in pressure could be caused by mineral deposits inside the expansion valve. The fact that your vacuum breaker got fouled lends some credence to this theory. How's the hardness of your water? Have you tested it lately?

While you're servicing the vacuum breaker, it would be a good idea to clean the expansion valve. Turn off and unplug the machine, let it cool, then drain the boiler per the instructions in the manual. You'll have to unscrew the expansion valve partway to do this. Go ahead and unscrew it all the way in order to remove the lower part of the valve. There's a spring and a plunger inside. Clean the parts with a solution of distilled vinegar and wash off all traces off the solution off (soap and water will neutralize the ascetic acid.) If you can't clean off the mineral deposits, a replacement valve isn't expensive.

Reassemble the expansion valve and screw it in all the way. If there's a set of black marks on it, unscrew until the marks line up. If not, unscrew at least one full turn, fire up the machine and adjust so that max pressure is 12 BAR after running the group for 10-15 seconds or so. Mark the fixed and rotating portions of the valve so you can return to that setting after draining the boiler, servicing the valve, etc.

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txrpls (original poster)
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#8: Post by txrpls (original poster) »

Peppersass wrote: You don't need the entire assembly. You just need the moving parts inside, which are available as a rebuild kit from your dealer or LM USA at much lower cost. There are only three parts, which you can also buy individually: A shaft, an O-ring and a Teflon seat. Usually the only thing that really needs replacing is the O-ring, which gets hard and/or caked with mineral deposits. Buy a supply.

The shaft and seat can usually be cleaned off, but it's not a bad idea to buy a couple of each just in case. Probably a good idea to get a supply of copper washers, too. They're usually reusable, but good to have just in case. Used on a lot of fittings in the machine.
I just ordered the whole assembly and parts to rebuild the old unit. I'll replace, rebuild and swap out as needed
Not sure about the boiler pressure, but the increase in pressure could be caused by mineral deposits inside the expansion valve. The fact that your vacuum breaker got fouled lends some credence to this theory. How's the hardness of your water? Have you tested it lately?
Waters fine. I use RO. Checked the steam boiler with a bore scope and there is very little build up.
Reassemble the expansion valve and screw it in all the way. If there's a set of black marks on it, unscrew until the marks line up. If not, unscrew at least one full turn, fire up the machine and adjust so that max pressure is 12 BAR after running the group for 10-15 seconds or so. Mark the fixed and rotating portions of the valve so you can return to that setting after draining the boiler, servicing the valve, etc.
Curious about the 12 BAR? I used a Scace and set it to about 9-10 BAR. It holds pressure during the entire shot both at the group head gauge and the coffee boiler gauge while pulling a shot.

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Peppersass
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#9: Post by Peppersass »

Not sure what you're asking about 12 BAR. Allow me to clarify:

12 BAR refers to the expansion valve setting, not brew pressure, which is set via the bypass valve on the pump.

The proper procedure for setting brew pressure is to run the brew cycle in free flow (no PF or Scace) and adjust the bypass valve on the pump for a brew boiler pressure reading of 9 BAR. Again, this is an adjustment to the bypass valve located on the pump, not the expansion valve over the drain box.

When you set the pump for a free-flow boiler pressure of 9 BAR, and then pull a shot, the brew boiler pressure gauge will rise to about 10-10.5 BAR due to the added resistance of the puck. But the pressure at the puck will be 9 BAR. You can measure that with your Scace. The 1-1.5 BAR drop is due to the gicleur (flow restrictor) between the boiler gauge and the group.

The expansion valve, on the other hand, is adjusted to prevent over-pressure when the boiler reheats. To set it, you run the group in free flow for 15 seconds or more, then turn it off. As the boiler reheats, the pressure will rise. Adjust the expansion valve so that it just hits 12 BAR maximum on the brew boiler gauge.

txrpls (original poster)
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#10: Post by txrpls (original poster) »

Peppersass wrote:Not sure what you're asking about 12 BAR. Allow me to clarify:

12 BAR refers to the expansion valve setting, not brew pressure, which is set via the bypass valve on the pump.

The expansion valve, on the other hand, is adjusted to prevent over-pressure when the boiler reheats. To set it, you run the group in free flow for 15 seconds or more, then turn it off. As the boiler reheats, the pressure will rise. Adjust the expansion valve so that it just hits 12 BAR maximum on the brew boiler gauge.
I swear the brew pressure gauge never hit 12 BAR the entire time I've had the machine. At least I have never noticed it that high. I will turn it back to the black marks. Just to be clear 12 BAR indicated is OK at the gauge as long as it is adjusted with the expansion valve?

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