This is my first post, I would like to say "Hello" to this great HB community, many thanks for all helpful information that introduced me to espresso world and helped me on my learning curve.

I have purchased 2-nd hand Nuova Simonelli Oscar, my first upgrade to HX-league.
Machine is several years old with CEME pressure-stat and valves.
First couple of tests worked well. Then a problem occurred.

After I press "turn on" button heat light just flashes for a second then pump starts. Without any delay immediately after pump starts I can see all water running through 3-way solenoid valve to the drip-tray. It runs without interruption approximately 90 seconds until safety timer turns the pump off and "empty tank" light is turning on. Shut it down, turn it on and everything happens again.

I would appreciate all suggestions and tips what can cause this problem.

I would like to diagnose and find the problem first, as I understand that attempting some disassembling/deep cleaning etc. may possibly cause more problems not solving original one.

Thank you!

It sounds like the group solenoid ("3-way valve") is stuck. See part #10 below.


See 'Hydraulics diagram' on Nuova Simonelli Oscar product page

Thank you for a suggestion. I think it was severe scale obstruction which caused the problem, as for now, solved by deep cleaning and repeated descaling/ backflushing. Hydraulics of the old 2nd-hand Oscar seems to work correct.

New problem: boiler cycle time.
Boiler is heating up well, there are no leaks. I do steam purge to release false pressure (no vacuum breaker on my model). After full heat up (even if I wait more then an hour) all seems to work correct, but boiler cycles very often. I did not measured it, but I would say, during idle time it turns on every minute or so for just several seconds. Is it normal? If I start to steam or brew water, boiler goes on almost immediately. Pressurestat is adjustable (made by CEME). Adjusting screw of the pressurestat works, I don't have instruments to measure temp/pressure (I will get what is needed soon), but as I can judge from steam power and brew water, boiler is getting to higher or lower pressure by adjusting the pressurestat, but regardless of pressure setting, boiler behavior is the same, very frequent cycles.

Questions:
1. Is that a pressurestat failure?
2. Can it be caused by a thermostat, electric connections or something else?
3. If I would need to change pressurestat, should I go for Sirai, or CEME/Parker/Mater/other will be sufficient?
4. Is it possible to fit bigger pressurestat as Sirai or Parker on the Oscar boiler without taking the boiler out of the case/frame?
5. I can't find more precise instructions/photos how to upgrade the Oscar with vacuum breaker. Where to put it on the boiler? Please help!

Thanks to everybody, have a nice day fellow coffee lovers!

Is it normal?

Yes. Below is a graph of a different machine but should be somewhat similar to yours. Please do not adjust this pressurestat without the benefit of an accurate gage attached to the steam arm for convenience.

Hello, thank you for response. I have just made simple gauge attachment to Oscar's steam wand, which proved boiler pressure/temperature to be stable and correctly adjustable by CEME pressurestat. I have started adjusting from 1.3 bars (initial setting), finished at 1.1 bars. It seems to give good steam power and HX temp surfing. Brewing water temps were measured by Styrofoam cup/milk thermometer. I will verify with thermocouple sensor as soon as I get one.

For those who might be interested (steam wand pressure gauge attachment):
Parts used:
- manometer up to 2.5 bars (scale in kPa)
- standard water intake rubber hose for washer machine (certified for up to 200F temp and up to 10 bars of pressure)
- two small hose claps
All parts were purchased in a local hardware store for less then 20 USD in total. Takes just couple of minutes to assembly. Make sure to prime the hose with cold water before connecting to the steam wand. Disclaimer: dangerous, attempt on your own risk!