La Marzocco GS/3 MP steam boiler problem

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

#1: Post by DaumierS »

For some time, I felt there might be a leak in my steam boiler. My machine used a lot of water, I needed to refill the tank every day.

Now, there is no steam at all. Dead. I guess the board shut down the steam boiler. No steam, but when I push the "tea" button, I have cold water.

But the machine uses an adequate amount of water now, and the espressos are still great.

There is no visual sign of any leak though. Very clean inside. Just the boiler is cold.

What could it be? Do I need to replace the steam boiler? This might be quite expensive (How much?), but I read that the steam boiler failure is highly unlikely with LM. So, hopefully it is something else...

Thank you!

DaumierS (original poster)

#2: Post by DaumierS (original poster) »

Some topics suggest that it might be an SSR problem, but how do I get access to the SSR's? I removed two side panels and I do not see them.

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#3: Post by EricC »

The SSR's are along with the main motherboard inside the black plastic box underneath the machine accessible from the rear.

See here : Post No.36

Water in La Marzocco GS/3 Brain Box

DaumierS (original poster)

#4: Post by DaumierS (original poster) »

I unplugged my GS/3, and used my multimeter to measure the resistance of two wires powering the heating element of the steam boiler. It shows "1" on the left, meaning infinity. Am I right in assuming that the heating element failed?

Should I just replace the heating element and the gasket? It looks like the cost of such a repair will be minimal, only $200 or so. But I am not sure if I identified the problem correctly.

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#5: Post by Jake_G »

You have to remove the wires from either the SSR or the element before you can confirm the issue, but if you have zero continuity/conductivity that is bad news for the element.

The remaining question is "why did it fail?".
LMWDP #704

DaumierS (original poster)

#6: Post by DaumierS (original poster) »

I think I identified the problem. Still waiting for the heating element for my steam boiler to arrive, but what caused the problem in question?

I tried to drain the steam boiler, but apparently it was empty. No water. When I disconnect the water level probe from the boiler, though, the pump starts to fill it with water. When I connect the probe back, the pump stops.

Am I right in assuming that the water level probe was always telling the board that the boiler is full (though in fact it was empty) and the element was heating the air? And this is why it broke? If yes, all I need is to replace the water level probe (after replacing the heating element as well).

Thank you!

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#7: Post by Peppersass » replying to DaumierS »

Did you mean to post this in a different thread? It's the first you mentioned a problem other than the vacuum breaker, which has nothing to do with heater or level probe problems.
Moderator Note:
This post and the preceding post were moved from a different topic to the current topic.

That said, if I understand the symptoms, your diagnosis sounds right. Pretty sure the heater can break if it's run continuously with no water in the boiler, but I would think the firmware would shut the heater down after a certain amount of time passes without the temperature probe getting to the target steam boiler temperature. Maybe not?

So, why is the probe not working? When the boiler is empty or the water is below the level probe, the probe is ungrounded (essentially, it's a bare wire sticking into the boiler.) That tells the CPU to open the autofill solenoid and turn on the pump. When water reaches the probe, minerals in the water short the probe to ground. That tells the CPU that water has reached the desired level. When you remove the connector on the level probe, it becomes ungrounded and autofill is initiated. When you did that, you proved that there's nothing wrong with the connector or wire or logic board.

That leaves the probe. I would guess that there's a lot of scale buildup on the probe and it's shorting the probe. It's not common, but it can happen. Best thing to do is remove the probe and inspect it. Unscrew the probe using the large nut that's right against the boiler, not the smaller nut that secures the probe inside the plastic sleeve. If you see a lot of scale on the probe, give it a good soak in distilled vinegar, wipe off the scale (or use a Scotch Brite pad to remove tough deposits) then rinse it thoroughly with water. If you don't see a bunch of scale on the probe, or if it still doesn't work when you reinstall it, the connection between the probe and the spade lug may be broken. I've never seen that happen, but I guess it's possible. If you have a DMM, VOM or continuity meter, you can check for zero ohms between the probe and the spade lug. If the connection is broken, you'll need a new probe.

DaumierS (original poster)

#8: Post by DaumierS (original poster) »

Again, the water level probe itself is pretty clean, but I gave it a rinse with a white vinegar anyway, and then rinsed.

I measured the connectivity, and the resistance between the end of probe and the spade lug reads about 0.4 om. Does it mean that the probe is functional? I inserted the probe back.

But the phenomenon is the same after cleaning. Disconnecting wire from the probe engages the pump. Reconnecting probe wire stops the pump.

But I realized that I did not actually drain the boiler due to a clogged drain pipe. I cleaned it with a nylon tube brush, drained the boiler. When I turned the machine on the pump started to fill the boiler, and stopped when it was full.

This can be a partial explanation to what I wrote before, I guess. When I connect the water level probe, since there is actually water in the tank, the probe stops the pump. So, the problem might not be in the probe.

Let me recall that the there is no connectivity in the heating element itself, the resistance is infinity. But probably the water level pump has nothing to do with it... So, the question remains: why did the heating fail? What I am afraid of is that after I replace the element, it might fail again for the same (yet unknown) reason.

DaumierS (original poster)

#9: Post by DaumierS (original poster) »

So, at the moment the only thing I know - the heating element is dead. I guess, I will just replace it and see how it goes...

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#10: Post by Peppersass »

0.4 ohms is probably the resistance of your meter probes, so for all intents it's zero ohms -- i.e. no problem with the probe connection to the spade lug.

Besides, you proved that by draining the boiler.

If you disconnected the wires going to the steam boiler heating element, and you get infinity ohms, that could indicate the heating element is broken. But there are other possibilities:

1. Have you checked the thermal protection device mounted on the upper right side of the boiler? One of the wires might have been inadvertently disconnected or has a loose/faulty connection. Or, the device might have tripped, which will shut off current to the heater (and give you an infinite ohms reading.) The red button will be popped out if it tripped. You can reset it by pushing the red button back in. If the boiler then heats, watch carefully to make sure it doesn't pop out again. If it does, there are two possibilities: 1) the boiler is overheating due to a bad temperature probe or water-contaminated logic board, or 2) the thermal protection device is faulty and needs to be replaced (I vaguely recall this happening on my machine...).

2. One of the wires is broken or a connection at the heating element has come loose or failed. You should check the resistance of each of the two wires from the brain box to its connection at the heating element. You should get zero ohms. If you don't get zero ohms, the wire is broken, perhaps at the connector, or the connection to the element is broken. I think you can pull back the heat shrink to get at the connections.

If it turns out to be the heater, best practice is not to reuse the boiler seal. You should replace it. Did you order one?