La Marzocco GS3 steam pressure going over

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
rahimlee54

#1: Post by rahimlee54 »

like the title says fired up for a coffee tonight and the steam pressure went almost to 3, the set max is 1.5. Any advice on DIY fixes or just call the repair company? Tech services mentioned heating issues so I thought about a new heating element but was looking for input.

Thanks
Jared

nahau

#2: Post by nahau »

Tech support probably mentioned heating issues because to create the higher pressure your boiler must be overheating. Your machine uses a temp sensor to control the heating of the boiler. If the sensor is dirty or faulty it might cause the boiler to overheat and create too much pressure. I would look at the sensor before thinking of a new element... seems the element might be fine. Note that I know next to nothing of how your machine is configured or runs... just what I read about it and common knowledge of how boiler pressure works.

rahimlee54

#3: Post by rahimlee54 »

Thanks for the reply sir. I started thinking about that as well. I'll drain the boiler and pull the element and sensor to verify.

Thanks
Jared

nahau

#4: Post by nahau »

Probably checking the sensor should be enough as the heater is probably ok. But, if you're gonna do it for curiosity's sake, then go for it! :D

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Jake_G
Team HB

#5: Post by Jake_G »

No real need to take anything apart.

Depending on the year of construction and the firmware installed, the GS/3 displays the heating element status on the display. On all but the oldest firmware versions, there are two boxes between the temperature and the time. I believe the left box indicates the coffee boiler heating element and the right box indicates the steam boiler element.

If the box is staying illuminated while the steam boiler is over pressure, you indeed have an issue with the temperature probe. It could be the cable, the probe or the logic board itself.

If the indicator is not illuminated when the boiler is over pressure, the logic board knows that the steam boiler is at or above the target temperature, but apparently the heating element is staying engaged when it is not being asked to.

In this situation, the most likely culprit is the solid state relay, which lives in the electronics cassette in the rear of the machine. You can check the relay visually while the machine is powered on and see if the little red light on it is illuminated or not. If the light stays illuminated, but the display shows otherwise, you likely have a short on the logic board that is keeping the SSR contacts closed. If the light is off but the heating element has voltage on it, the SSR is likely failed closed and needs to be replaced.

Another possibility is that the steam boiler if over-filled and this is causing the pressure to climb too high when the boiler is attempting reach the target temperature. Situations with over-filled boilers are almost always caused by water contamination on the logic board.

Take a look at your display and let us know what you find.

Cheers!

- Jake

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Peppersass
Supporter ❤

#6: Post by Peppersass »

As always, Jake's advice is spot-on. Some additional comments on what to do after checking the boiler heating indicators on the display:

- Turn off, unplug and let the machine cool completely before proceeding.

- First thing I would do I is remove the side and top covers, then carefully check for any signs of a leak inside the machine. Look for any water or mineral deposits on the chassis floor, fittings, boiler seals, etc. If you see any signs of a leak, or if the temperature probe checks out OK, you need to check whether water has gotten into the brain box. Go to the last paragraph for instructions. You will also have to locate the source of the leak and fix it.

- (Jake, please comment on whether the following is reasonably safe to try): If you don't see any signs of a leak, try swapping the coffee boiler and temperature probes. I believe other GS/3 owners have tried this approach to checking the probes. I would run the experiment only long enough for the steam boiler to come up to temperature, which should happen before the coffee boiler hits the target temperature. I believe it's safe because if the coffee boiler overheats, the expansion valve should release the excess pressure. Obviously, if the steam boiler continues to go over pressure, there's a problem with the temperature probe wiring, the SSR or the logic board.

(Speaking of over pressure, the steam boiler OPV (in the can between the boilers) is set to release excess pressure at about 3 BAR. If the boiler got all the way to 3 BAR before you shut off the machine, and the OPV didn't trigger (you would hear the noise of steam escaping into the drain box), then your OPV should be replaced.)

- Although the temperature probe is a likely candidate, Jake is right that failures like this can be caused by a water-contaminated logic board. Often the board can be saved, but in some cases it has to be replaced, which is expensive (about $600.) If you determine that the probe isn't the problem, go to the last paragraph for instructions on checking for water contamination in the brain box.

INSTRUCTIONS FOR CHECKING THE LOGIC BOARD: Remove the rear cover, pull out the brain box, remove the cover (careful -- it's easy to lose the small screws or washers), and look for any signs of water or mineral deposits on the logic board or in the brain box. If you suspect water has gotten in, and you're OK with working on wiring, take a photo of the board, label each connector so you know where it goes, then remove the connectors so the board can be unscrewed and taken out. Check the underside of the board and the floor of the box underneath. Dry up any water inside the box and remove any mineral deposits. Dry the board if necessary and clean it with 90% or 99% isopropyl alcohol, making sure to remove any mineral deposits. Allow the board to dry overnight. I put mine in a bag with rice, but some argue that it doesn't quicken the drying. Reinstall the board, referring to the photo to make sure you have all the connectors in the right place and properly seated. Put the cover back on and screw it down, making sure not to pinch any wires. Push the box back into the machine, put the back cover on and screw the cover and box to the chassis. If you have any issues with the display or buttons, it's likely that one or both of the ribbon cable connectors pulled off the logic board when you pushed it back in. You'll have to reopen the brain box to reseat the connectors, then shove it back in taking care to keep the ribbon cables from being yanked.

Hope this helps and hope it's not a leak.

mk3

#7: Post by mk3 »

"Situations with over-filled boilers are almost always caused by water contamination on the logic board."

or a bad check valve letting water flow backward into the boiler.

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Jake_G
Team HB

#8: Post by Jake_G »

Touche!

Having had the second check valve added to my machine before I received it, the faulty check valve situation is one I sometimes forget about. But yes, if both check valves leak on a "modern" GS/3, you can certainly fill the steam boiler to the brim without any logic board issues at all. (Though the ensuing water storm inside the machine can certainly cause some logic board issues...)

Single check machines are obviously plenty susceptible to simple overfilling during normal operation.

Cheers!

- Jake