La Marzocco GS3 builds up steam pressure to 3 bar ...

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MichaelSchneider

#1: Post by MichaelSchneider »

Hi out there,

My La Marzocco GS3 suddenly started to build up steam pressure all the way to the end of the scale which is 3 bar. If I release the pressure it stays around 1,5 - 1,7 .... for a while at least. When I turn it on in the morning it builds up to way past 2 bar ...

Can I adjust the pressure somewhere? Or ist there some valve that needs to be cleaned / descaled ?

Best Michael

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Jake_G
Team HB

#2: Post by Jake_G »

Your vacuum breaker is stuck closed.

Usually when they need service, they leak a bit and you get a constant dribble of steamy water out of the hose into the drip tray, but they can also get stuck in the closed position.

I believe this occurs when the teflon insert has worn out far enough that the O-ring on the plunger "pops" into it like a ball socket.

This post by Dick shows all the bits and pieces 8n the vacuum breaker valve:
La Marzocco GS3 vacuum breaker cleaning?

When I experienced high pressure like you are, I was able to temporarily resolve it by cleaning the components, but ultimately I ended up replacing the O-ring with a fatter one made from Aflas. The original O-ring kept sticking in the white insert, and I had good luck with the fat O-ring, so I reverted back and haven't had any issues since. I suspect that I could have replaced the insert and been good to go, but I had lots of O-rings on hand and no spare inserts.

Cheers!

-Jake
LMWDP #704

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Peppersass
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#3: Post by Peppersass »

I wasn't aware that a stuck vacuum breaker can cause pressure to rise above the target setting. Why does air in the boiler cause this to happen? Why doesn't the OPV trigger?

My previous understanding was that without a vacuum breaker, air in the boiler would come out of the steam wand with a massive "pop" the first time it's used after warmup. It's scary but harmless. I think I've seen advice that if the breaker needs service you can temporarily remove it and close off the opening. Sounds like that's a bad idea.

Michael, you say that you can release the pressure and it stays at 1.5-1.7 BAR, at least for a while. I would think once the air is release, the pressure will stay where it's supposed to be until the next shutdown/warmup cycle. Are you saying that after you release pressure it eventually builds back up, or does this only happen when you restart the machine after letting it cool down?

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Jake_G
Team HB

#4: Post by Jake_G »

Peppersass wrote:I wasn't aware that a stuck vacuum breaker can cause pressure to rise above the target setting. Why does air in the boiler cause this to happen?
On pressurestat machines, the "false pressure" trips the pressurestat early and the boiler fails to reach operating temperature, but the pressure remains at the setpoint.

On a PID-controlled boiler, the heating element will stay on until the boiler reaches target temperature, and the "false pressure" will be additive to the saturated steam pressure in the boiler. In my case, this was just about 3 bar.
Peppersass wrote:Why doesn't the OPV trigger?
My guess is that the OPV is set just a smidgen higher than what this scenario causes. That, or it cracks and vents down to 3 bar, but I never heard a release.
Peppersass wrote:My previous understanding was that without a vacuum breaker, air in the boiler would come out of the steam wand with a massive "pop" the first time it's used after warmup.
That's more or less correct. I'd just crack the toggle and bleed the air off with more of a whooshing hiss than a pop, but hot air at 3 bar has some oomph to it. That's for sure.
LMWDP #704

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Peppersass
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#5: Post by Peppersass »

Thanks. I just realized what your avatar is. So appropriate :D.

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cannonfodder
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#6: Post by cannonfodder »

PID and pressurestat machines behave differently. Vacuum breaker valves are one of those consumable parts you want to have a spare. That also reminds me that I do not have a spare for my GS3. Probably should order one for the parts drawer. LM developed a new style valve. If you have the older one upgrading may be a good option.
Dave Stephens