Rocket Appartamento temperature drops and holds post shot

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#1: Post by dhowe »

I recently purchased a second hand Appartamento that the first owner had a few months. I have since installed the group head thermometer and have been getting consistent temps. The issue or suspected issue is that once I pull a shot I flush the shower screen as usual. If I dont touch anything after the shot the temperature will continue to drop until I flush more water to "wake it back up". I pulled a shot this morning and left it for almost 2 hours and the thermometer was in the 60ºC range.


#2: Post by JRising »

I'm answering this with the understanding that your boiler temperature/pressure remains okay, somewhere in the 0.9 to 1.3 Bar range, and that the issue is just that the grouphead thermometer is showing that the grouphead isn't heating. Correct me if the boiler is also dropping over time.

So, it's a thermal stall sort of situation. Normally the boiler heats the heat exchanger to above boiling. This extremely hot water is lighter than the warm water in the E61 head, so the extremely hot water flows upward, out through the top fitting of the exchanger, into the top fitting of the Grouphead while at the same time the warm water is flowing down from the group head, out the lower fitting of the group head, into the lower fitting of the heat exchanger and replacing the water that has flowed upward.

If there's calcium blocking one of the pipes between exchanger and head, then this thermosiphon flow can't happen.

If there's a leak in the brew circuit, then the extremely hot water is going to expand into steam and force the brew circuit's water out through the leak. once some water is gone from the system then you have extremely light steam in the upper half of the circuit, heavy water (Not Deuterium oxide, just liquid water that's heavier than steam) in the bottom and although there's a bit of condensation in the head, the flow is so little that the head won't stay hot, the liquid water just won't rise high enough to create the syphon effect against the pull of gravity.

If this is the case, a leak from the brew circuit, it could be leaking over the brew valve (possibly noticeable as a drip from the drain valve while the machine is idle), a leak from the expansion valve (Normal when the machine is heating, but if it still drips after everything's fully heated then it's a leak), or it could be leaking backward through the pump or bubbler/priming valve (noticeable because the priming valve will be hot from the heat exchanger water flowing through it).

Your turn. Let us know what you find.

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dhowe (original poster)

#3: Post by dhowe (original poster) »

I am still very new to the E61 so I'm not sure how often the pressure stat should be kicking on and off. I just went and looked at the machine after running a flush about 15 minutes prior to try to get the temps back up and there was a pretty constant drip from the drain valve. I waited a few minutes and it has since stopped but the machine is holding temp at around 85C. I'm not entirely sure where the priming valve is so I will try to look that up.

dhowe (original poster)

#4: Post by dhowe (original poster) »

Thermosyphon Stall (Rocket Appartamento)

This user has described the exact same problem I am having. Any solutions would be appreciated.


#5: Post by JRising »

Okay, Thermal Stall situation. With some possible evidence of leakage through the E61 head.

Side note #1: If boiler pressure doesn't go below 0.8 bar and doesn't go above 1.4 bar, then your pressostat is working well enough.

Side Note #2: The bubbler valve/priming valve will be right on the outlet of the pump, it's an off-white plastic cylinder screwed into the pump outlet with a silicon tube connected to a port coming out the side. If this is very hot after the machine's been on for a while, then this is where your HX water is escaping. Read the paragraphs above, there are plenty of causes for thermal stall and at least 3 places other than a cracked heat exchanger for HX water to leak out.

Actual Answer: Let's chase down that leak from the drain valve since it may have made itself obvious...

Of course while the boiler heats to its maximum temp, the heat exchanger inside it gets heated. The water in the Heat Exchanger would try to expand because it's taking on that heat energy, but it is trapped because there is a check valve on the outlet of the bubbler valve that shouldn't let it flow back toward the pump, and the brew valve is closed when the control lever is down, so it can't flow forward to the grouphead.

But, if the brew valve leaks a little, then that HX water will expand and flow out through brew valve (the top most valve in the E61 head), of course, with the lever down, the pre-infuse and the drain valves are wide open, so when that water gets to the head it simply falls out through the drain.

One can PROVE that their brew valve is leaking by pressurizing the heat exchanger and brew circuit with the pump while the brew valve is closed. If water flows over the brew valve and out the drain, then the brew valve leaks, right? Press and hold the brew button behind the control level to have the pump try to force water through the brew circuit. You can use a soup spoon, slide it behind your lever so that the curve spoons with the cam that pushes the button, if you leave the spoon leaning against the E61 head, it will just stay there while you watch the drain. Don't leave it there for more than 30 seconds or so, the pump gets warm trying to run with no flow.

So above test done? If water flowed (or at least dripped) from the drain while the pump tried to force it through the brew circuit, then you've found where the water is escaping from the heat exchanger and that's why it gets its thermal stall.

dhowe (original poster)

#6: Post by dhowe (original poster) »

Honestly have no clue at this point. The primer valve did not feel overly hot, maybe warm just because of its location. I turned the machine off for a few minutes and turned it back on and waited about 10 minutes. The grouphead was sitting at 111C and pure steam came out for a good 15 seconds. Now I seem to be having the opposite problem.

dhowe (original poster)

#7: Post by dhowe (original poster) »

I did the spoon thing and nothing came out anywhere.

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#8: Post by JRising »

Copy/Pasted from the thread you linked:
- Short time (somewhere less then 5sec)
- No counterpressure (blind basket test)
- A heated up machine (I can't trigger the TS Stall when I flush a cold machine. It will heat up normally afterwards)

Is this what you're doing? Opening the brew valve and not allowing the cooling flush to purge the steam?

The heat exchanger is INSIDE the boiling boiler. When allowed to idle, no water in, no water out, the water inside the heat exchanger will in 10 to 15 minutes get far too hot, it will exceed boiling temperature. After 15 to 20 minutes of idling, the HX water will be around 120 C. When you open the brew valve (raise the lever) that very hot water is going to expand rapidly into steam. That steam is going to flow out through the brewhead fairly rapidly, while the pump is pushing replacement water slowly into the heat exchanger. The steam can blow through the gigleur much faster than water such that although the little vibe pump is trying, that superheated water is going to expand to steam and blow out until the pump has replaced a significant portion of the HX's volume. If you just do a short little cooling flush, really just letting a quarter of HX water boil and escape rather than bring the HX down to just below boiling temp, then your HX ends up as a traditional boiler. The upper quarter is a steam pocket rather than superheated water forcing the thermosyphon flow. The water sits heavy in the lower pipe, steam fills the upper pipe and other than the slightest condensation at the mushroom, there's barely any flow. Even when hot, liquid water isn't going to flow uphill into lightweight steam.

dhowe (original poster)

#9: Post by dhowe (original poster) »

I'm just going to explain everything that I do when pulling a shot so you can get more information. I am currently using a fan as I have seen someone else use to cool the group head. I cool the group head to 89C with the fan and it will continue to drop and I then catch it on the upswing and start the shot once it reaches 89 again. This is the easiest way I have found to get a very consistent temp without going through gallons of water. Once the shot finishes I do a screen flush to remove the excess coffee and replace the portafilter. At this point the temp starts dropping unless I flush some water to get it back up. Hopefully using the fan to cool the group rather than cooking flushes isn't causing adverse problems. Thanks very much for the help. I would call WLL or someone but as I bought this machine second hand they won't warranty anything. Tomorrow when I pull my first shot I will do the cooling flush and try to pull shots from there. Boiler is set to around 1.1 at the top and above .9 at the bottom.


#10: Post by JRising »

Maybe that's going to be similar to using the machine in a very very cold room. I don't know if it's the same, but when I use the cottage machine after arriving in the winter, the machine heats up in about 45 minutes, the cottage takes a couple hours and during that second hour the machine does make some pretty sour coffee. I don't know if it exhibits thermal stall symptoms. I still think you're letting the steam out without letting the heat exchanger fill when you're messing with the lever. That's the same as leaking over the brew valve, only it's not a leak, it's someone lifting the lever.