La Marzocco GS3 MP -Steam boiler reads over 3bar cold

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

#1: Post by pgopinath »

I have read through all the threads related to the steam boiler on a GS3 MP reading over 3bar and the guidance that the vacuum breaker valve was stuck closed.

My GS3 has the conical valve modification though I don't think that is pertinent to the problem I am experiencing. It is also plumbed in.

My GS3 started showing 3bars on the steam gauge a few days ago. When I pulled the steam lever the pressure would drop to about 1-1.5 bars but I was getting a lot of hot water and not good steam. Assuming that it was a bad vac breaker I replaced it with a new spare.

I turned on the water to the machine with the machine off. The steam gauge immediately jumped to over 3bar and a steady stream of water came into the driptray by way of the clear plastic tube attached to the vacuum breaker valve. I don't recall ever seeing this behaviour before so I didn't bother to turn on power to see whether this would correct itself.

Does anyone have any ideas on additional diagnostics I could perform to figure out what the problem might be?

Possibly unrelated question: what is the part with the toothed wheel on it on the right side of the machine?

Thank you.

pgopinath (original poster)
Supporter ♡

#2: Post by pgopinath (original poster) »

Ignore the question about the toothed wheel. I don't recall ever having used the hot water dispenser so I had forgotten that the toothed wheel was accessible behind the side panel to mix water temp.

I am beginning to think that the steam boiler solenoid valve may be stuck open.

With the machine completely disconnected from power when I open the external valve to the plumbed in water line the steam gauge immediately jumps to 3 bar and water streams out of the vacuum breaker line and the OPV line. This tells me the steam boiler is full and that it is getting pressurized to water line pressure when I open the valve.

I would be grateful for any thoughts or suggestions.

User avatar

#3: Post by HB »

That's exactly what I was thinking too, i.e., the steam boiler fill solenoid isn't closing. Eventually the steam boiler will fill to the top, the gauge pressure will rise to the plumbed-in line pressure when idle and peg if the pump's refill cycle runs. Water will run out the vacuum breaker and water flows freely out of the steam wand.

That happened to one of my espresso machines that had sat idle for a long time. Soaking the solenoid valve in vinegar to remove the scale/grit preventing it from closing completely resolved the problem. The refill solenoid is a normally-closed valve, so presumably it's not a matter of the coil not working.

See About 3-way Solenoid Valve Operation for some helpful discussion and photos.

Three-way solenoid valve plunger
Dan Kehn

pgopinath (original poster)
Supporter ♡

#4: Post by pgopinath (original poster) »

The problem has been resolved. I somehow found a LM GS3 Parts Manual V3.2-2018 on my computer. I took apart every copper line leading into the steam boiler on the RHS and thus identified which was the water fill line. I confirmed that water was indeed flowing into the steam boiler as soon as i opened the external shutoff valve on the fill line.

Per the earlier post i took apart the water fill solenoid and found that it was a gunky mess from sitting around. one hour in vinegar cleaned it up nicely. After putting it all back together everything works as it should.

Thanks everyone!