La Marzocco GS3 Wet Steam

Need help with equipment usage or want to share your latest discovery?

#1: Post by Waldo »

I am puzzled ..... I have a LM GS3 (01/12 Built date) and from one day to the other my steamer produces saturated water instead of high pressure steam. The steam boiler pressure gage shows 1.6 Bars. The steam nozzle holes are clean. What could cause this issue? Appreciate any inputs ... thanks


#2: Post by sluflyer06 »

Are you saying it produces water, akin to the hot water tap?

If so, sounds like it's overfilled to me, what happens if you use the hot water tap until the pump kicks on and immediately open the wand? Do you get steam now?

Waldo (original poster)

#3: Post by Waldo (original poster) »

Wow, you are absolutely correct with your diagnosis. Thanks so much. Now, do you happen to know how the boiler could overfill (first time in 10 years of daily use) and how I can prevent this from happening in the future?

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#4: Post by Peppersass »

There are several possible causes of steam boiler overfill:

- Insufficient mineral content in water. Minerals in the water allow conductivity between the probe and the boiler, which is grounded. So, when water reaches the probe, it's grounded to the boiler and frame, which signals the CPU to stop filling. If you use RO or water with very low mineral content, it won't conduct and the boiler will overfill. There's a probe sensitivity adjustment in the OFF menus that can be set to Lo, Med or Hi (I think), that sometimes be adjusted to compensate for low mineral content.

- Probe disconnected. If the probe isn't connected to the CPU, the ground signal won't get through and the boiler will overfill. This could happen if the probe connector is very loose or corroded, or if the wires somehow got damaged, possibly by someone working on the machine. This isn't a common cause of the problem, but it's easy to check.

- Scale buildup on probe. This can isolate the probe from the water, making it impossible for the probe to be grounded by the water. Turn off the machine, unplug it, let it cool completely and carefully remove the probe from the boiler (unscrew the large outer nut, not the smaller inner nut.) Examine and clean the probe. As the machine is old, the fiber gasket may not seal properly when you reinstall the probe. If not, you can use Teflon tape on the threads as a temporary measure until you get a new fiber gasket. Just be sure not to let any of the tape get inside the boiler.

- Contaminated logic board. Due to the layout of the GS/3 components, any leak inside the machine can lead to water getting into the brain box, which located under the steam boiler. Water can wick along wire cables leading into the box, or it can seep through holes in the chassis and thence into the screw holes of the brain box. If water gets on the logic board, it can cause strange behavior, and overfilling of the steam boiler is one of the known things that can happen. To check, first turn off the machine and unplug it. Remove the side and top covers, and carefully inspect inside for any sign of a leak. That can include pools of water, drops of water, dried minerals (usually white or green), etc. Check the floor of the chassis and all fittings. If you see any signs that water has leaked inside the machine, remove the two screws at the bottom rear of the machine, remove the back cover and gently slide out the black plastic brain box. Unscrew the cover and gently lift it enough to get to the wires connected to the rear panel switch. Take a photo of the wire connections to the switch, then disconnect the wires so you can get the cover the rest of the way off. Look for any signs of water in the brain box, including dried mineral content, and carefully inspect the top of the board for any water or dried minerals. Even if you see nothing, there could be water under the logic board. To check for that, you have to remove all the wire connected to the board. Take a photo first and label the wires to make sure you plug them back where they belong. Unscrew and remove the board to check underneath. If you find water or dried minerals, dry off the board and clean it with 90% isopropyl alcohol. NOTE: You must find and repair the source of the leak before using the machine. Otherwise, the logic board will get contaminated again.


#5: Post by mk3 »

Another likely cause is a bad check valve.

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#6: Post by Peppersass »

Forgot about that one. Does your machine have the update where they added a check valve to the steam boiler hot water output? They replaced the single tube leading from the mixing valve to the steam boiler with two tubes and a check valve between them. The idea is if the check valve on the mixing valve fails, the second one will protect the boiler from overfilling.

If your machine doesn't have the update, then you should inspect the check valve on the mixing valve. If it's compromised, replace it. In any case, get the update so you have belt and suspenders.