Nuova Simonelli Oscar II: Anti-vacuum valve flooding

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

#1: Post by Organistespresso »

Hello all! Have been following this forum for a while as I got my first espresso setup and loved all of the great advice on here. I am having a bit of a problem that I hope someone may have either encountered or have a solution too.

I bought a used Oscar II a few months ago and it's been running great, until it started to puddle underneath the machine. I took it to a local shop where they replaced the connection from the water tank to the boiler, and replaced the heater probe, but when I got home it started leaking within two days again. I went ahead and opened it up and the problem was immediately clear, the anti vacuum seal is flooding while the boiler is heating up. It drains once the boiler is stabilized, but then will flood again during the next heating process. Photo attached, it is hard to tell but the valve is completely full of water.

Any idea what is going on with this? The shop already charged me a fair amount for the repairs they did, and I hate to take it back there and get charged again if it's something that they have not been able to diagnose and fix correctly.


#2: Post by CSME9 »

Probably need to change the anti v valve, easy to do. They tend to get scaled inside, you can try to take apart and clean the teflon washer but best to replace entire valve/inexpensive part. If you have the clearance suggest you buy the type with a barbed end that bleeds out-you can connect a silicone hose to it so it drains to drip tray or water tank. That way if it sputters water out it doesn't get all over/wet the inside of machine.


#3: Post by WWWired »

Interesting issue :)

Don't go back to that shop . . . folks here like CSME9 are far better and will diagnose and solve this issue in no time :)

CSME9 had a solid suggestion to attempt for sure. How often do you descale is a question to consider. Of course descaling doesn't really reach the Antivacuum Valve so CSME9's solution to replace it or attempt to remove and check/clean any scaling and mineral build up is excellent given that can be a problem depending on water quality. The Antivacuum Valve has one function: It allows air to enter the Steam Boiler vessel (not the HX Line) during a cooling phase. It is also possible, that water drawbacks from a leaky 2-Way Solenoid, due to a reduction in water volume during the cooling phase can create decompressions and suctions of water from the Water-reservoir or even from part of the feed to the HX Line, past an obstructed 2-way Solenoid and the one-way check-valves.

Additional Considerations If Not the AntiVacuum Valve:

Do you use the Steam Wand much? How is your steam pressure? If you do steam milk, how is the water quality you are getting from your Steam Boiler (the larger 2 Liter Soda bottle sized vessel)? . . . is it dirty/or does it have a bad odor? This would indicate a failed/obstructed AntiVacuum Valve as well that is possibly siphoning/suctioning small amounts of left over milk from the Steam Wand back into the Steam Boiler as the water volume decreases (due to cooling) inside the fixed volume Steam Boiler vessel. Do you hear a bit of noise coming from the Antivacuum Valve all the time when your Steam Boiler is at full temperature/pressure? (this is not the sound of tiny espresso machine citizens living inside your wonderful Oscar II sacrificially throwing tiny espresso machine animals into the Anti-Vacuum Valve Copper Volcano Cup, but could indicate an obstruction of the valve seat/seal as CSME9 identified above).

Might add to CSME9's descale recommendation: Unplug your machine, remove your 2-Way Solenoid (never remove a Solenoid/Electrovalve when powered/plugged-in), inspect the center Piston/Plunger assembly (the outer block Solenoid Coil is likely ok based on your description). Look for any calcification, mineral buildups or obstructions that would allow small amounts of water to bypass your normally closed 2-way Solenoid (when the coil is not energized) and trickle-extra drops of water into your Steam Boiler overfilling it over time.

*Edit: After reading cafeIKE's great comment (just after this one), here are some additional dimensions of the Boiler-Water-Level-Probe in support of the info cafeIKE mentioned that a boiler water level should be 60-65% of the internal diameter of a horizontal cylindrical Steam Boiler. Interestingly in the Oscar/Musica HX Boilers of this design, the elongated "C" HX Line that runs through the Steam Boiler has only the bottom leg of the C-shaped HX Line covered by the larger Steam Boiler vessel's water and the top leg of the HX-Line's "C-shape" is above the water surface in the steam, so in your instance, your extraction temperature may be affected by the complete submersion of the HX Line . . . you can see from the picture below, the Steam Boiler Water-Level-Sensor-Probe is part of a Circuit that detects continuity and when the Circuit is completed (by water touching the bottom-most tip of the Steam Boilers water sensor probe) the pump will stop and 2-way Solenoid will be de-energized (closing its orifices). The length from the bottom of the Water-Level-Sensor-Probe's wrench fitting (at the top of the threads) to the bottom of the sensor probe is 45 millimeters (1 3/4 inches). That is the closest water should come to the top of the boiler (a 60 to 65% fill as cafeIKE mentioned below, governed by the Boiler's Water-Level-Probe continuity-state). Two important items worth noting therefore: (1) The Pump should never be called to fill the Steam Boiler if water is touching the bottom of the Water-Level-Sensor-Probe; and (2) The 2-way Solenoid should never be energized (opening the Solenoid outlet port) when water is touching the Steam Boiler Water-Level-Sensor-Probe (creating continuity in the circuit) . . .

. . . and here is a picture of how scale/minerals can build up on a Solenoids "Body Orifice Seal," a 2 millimeter diameter hole in the center of a doughnut (that the Plunger presses down on when not energized/moved upward by the Coil) that is supposed to provide a watertight seal when the 2-way Solenoid is not energized . . .
. . . if there were significant buildup of minerals on the Body Orifice Seal, water could be pushed by into the Body Orifice Port, which is the direct connection from the 2-way Solenoid to the water line that fills the Steam Boiler, thus being one possible very subtle cause of an overfilling boiler. As an outside chance (rare) the Compensating Spring in the center of your 2-way Solenoids Plunger may have failed. If you do decide to take apart your 2-way Solenoid you will need to (1) remove the Solenoid Coil (the square block); then (2) Place the 2-way Solenoids nut back on the top of the "Stop" threads (the threaded part of the top of the plunger the nut screws onto); and then add another nut to the top of that nut (you can get the one off the 3-way Solenoid) to serve as a locking-nut when you turn out the lower nut of the two (counter-clockwise when looking down on it). This will allow you to use a wrench to turn the bottom nut and spin out the threaded Plunger "Stop" for disassembly of the entire central core.

Here's a picture of the 2-Way Solenoid disassembly issue relating to removing the central "Stop" without resorting to using a pair of pliers on it and damaging its surface . . .

. . . and finally, a picture of the Plunger "Stop,: the "Compensating Spring," Plunger and Coil . . .

All this being said, an important consideration for these amazing and incredible pieces of engineering and technological genius we call espresso machines, is they should likely be given a complete overhaul every-other-year, along with the regular weekly and monthly maintenance needed. Such an overhaul will include complete disassembly, for the more adventurous, and a deep clean of every part and replacement of needed components. Many times, these most impressive worldwide marvels we get our daily doses of espresso from can sadly be neglected for many years by busy owners, who certainly do not mean to do so, until finally, the machines reach a point of failure. At that point, we, the few, some of us amongst the multitude of poor, some of us technologically fascinated and wonder struck by espresso technologies, and others just refined aficionados of the incredible culture of coffee . . . at that point, we can open the car door of that Rolls Royce who's ashtrays being filled, was pushed off the side of the road by a member of the uber wealthy, or perhaps at that point we are called upon to provide a new adoptive home for the problem espresso machine child of otherwise engaged hard working people who are busily fighting to keep our world from plunging into anarchy . . . whatever the reason, we can be the inheritors and beneficiaries of these opportunities to come into contact with these incredible machines and enter a wonderful adventure into the inner world of high technology and engineering that are espresso machines.

User avatar
Supporter ❤

#4: Post by cafeIKE »

If that much water is coming out of the vac break, the boiler may be over filled.

Check the water fill level: Pull the vac break and measure water depth with bamboo chopstick, wood dowel or something that will show the water level.

On a round boiler, the water level should be about 60-65% of the boiler height.