Well the problem was painfully obvious. The probe was inserted as far as it could go! The reason for this is two-fold. One, the nut was a bit loose and the probe slides in and out easily. Two, the probe and it's wires are near the top of the machine right underneath the dull metal plate that protects the internals. I've removed this a few times and in the process no doubt knocked the probe further in the boiler. It's actually quite a silly design in this regard. Eric, perhaps you can tell me how far the probe should be in??

I also suspect the loose nut which holds the probe's sheath to be the source of a very slight hissing I hear occasionally coming from inside the machine.

Eric, perhaps you can tell me how far the probe should be in??

The electrical connection to the water level probe, in all the pics I have seen, is vertical and the "plastic" insulator is at or very near the top surface of the gland nut.

This makes it very convenient for the user as regards getting the height "just right" after servicing the probe.

I pulled the probe out a little last night in the hopes that would solve my lack of steam. Of course I wasn't thinking straight as that's opposite of what I should have done. Anyhow I woke up to a wet counter and kitchen floor this morning. At 6am when my timer kicked on the boiler overfilled so much that the vacuum breaker shot water all over the inside of the machine, counter, and floor. Nice. So I proceeded to fully remove the probe assembly. The probe itself was very clean, no problem there. I put everything back and inserted the probe quite low where I had originally noticed it yesterday. The pinched portion of the probe that the plastic connector attaches to is almost level with the plastic sheath and can't really go much lower. I turned everything back on and pulled a shot, then steamed. Seemed to go well but basically I have everything back in the same position as when I had problems so I'm slightly confused. I'll guess I'll just have to see how steaming goes over the next couple days.

Is there some technically correct way of setting the probe depth??

Is there some technically correct way of setting the probe depth??

No, because there is no hard core information (that is public) as regards the "design" water level of the boiler. Lacking this information, I would say that a water level of 2/3's of the boiler's internal dimensions could be considered reasonable.

The correct way to initiate steaming is, of course, to bleed the steam path of any condensation. Doing this should cause the pressure to drop enough such that the heating element comes on and stays on during the entire steaming process. But you need to appreciate all the factors that might enter into this "equation" - not just for you but for anyone.

a. heating element power - both advertised and real
b. size of the steam tip hole(s) - both as new and existing
c. quantity of milk one is trying to steam

Based solely on my very brief experience of steaming with a Rocket machine at 1.20 bar (max) and your description of what happened when you raised the water level - "I pulled the probe out a little last night . . ." - there exists problem(s) with your machine other than boiler water level.

How about measuring your existing water level by removing the vacuum breaker?

Thanks as always eric for the help! If over the next couple days I still notice streaming issues I will do just that. Question: Is there a difference in checking the water level via the vacuum breaker or the level probe assembly?

No, as long as you provide sufficient data that other Rocket owners can relate to. For example, if someone said, "my water level is 4.0 inches as measured from the internal bottom of the boiler after auto-fill has taken place", that sorta nails a value and the conditions underwhich it was taken.

OK great, and do you have any tips for how to measure this? Small holes and darkness in the boiler makes this tricky I imagine. Fashion some sort of dip stick? I suppose the preceding steps would be let the boiler fill, power off the machine and release all steam via the steam wand?

Have you measured the brew temperature to verify that the boiler's pressure gauge is accurate? You might be starting from a pressure even lower than you think. The water level is not just to maintain a "reservoir" of steam. I was told that the water stores a tremendous amount of thermal energy (water being more dense than the steam, something of which I have been accused). So there is a balance between enough space for ready-steam, and enough water to not only cover the heating element and HX, but also to store thermal energy.

As per my erics thermometer, everything seems in range.

OK great, and do you have any tips for how to measure this?

If you simply pull the water level probe out, that is too small a diameter and breakage is a possibility.

Remove the vacuum breaker.
Lightly sand a 1/8" wooden dowel to remove mill finish.
Power machine up from cold, let auto-fill do its thing, shut machine down and unplug.
Insert dowel, measure water level, making sure you hit bottom.
Double or triple check yourself, record value.

Have you ever changed steam tips? Steaming reponse really needs to be checked with the tip the machine was shipped with, assuming that is the tip the majority of current Rocket owners are using.