Nuova Simonelli Oscar II produces steam pressure but cold water at grouphead

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

#1: Post by Marthvader »

Hello everyone! I'm new here as I just acquired an Oscar ii for a steal. It's producing great steam pressure but the water at the grouphead stays around 140F. I've descaled the boiler and heat exchanger but the water coming through is still not getting hot enough. If anyone has any insight, I'd greatly appreciate it! Thank you!


#2: Post by bgnome »

What is the boiler pressure / temperature? How long are you waiting for initial warm-up?

Marthvader (original poster)

#3: Post by Marthvader (original poster) »

Thank you for reaching out! I've given it roughly an hour to heat up. I haven't measured those yet. Is there a good way to check the temp and pressure with household tools? Thanks again!


#4: Post by BogongTiger »

Marthvader wrote:... It's producing great steam pressure but the water at the grouphead stays around 140F...
The water from the grouphead is heated by passing via a copper pipe that runs through the boiler that produces steam. So it sounds odd that you'd be getting good steam without the grouphead water getting hot enough.

How are you measuring the grouphead temperature? Even if it's in the cup, which would be quite a bit cooler than the grouphead itself, it sounds low. Have you tried the styrofoam cup method outlined in this thread?
Seeking low tech way to measure brew temperature

Marthvader (original poster)

#5: Post by Marthvader (original poster) »

I've been holding a thermometer on the screen as the water flows out, but I'll give that a shot as well! Thank you

Supporter ♡

#6: Post by Nunas »

As far as I know, the Oscar II is a fairly ordinary heat exchanger machine. The only programmable feature on it is dose size; the temperature of the brew is not programmable, as there's no PID. If this is so, then the only things that can affect the temperature of the brew water are the pressurestat and the duration of the cooling flush.

Concerning the latter, if you've not used an HX machine before, be aware that it is normal for the first bit of brewing water to be too hot; it is therefore normal to do a cooling flush until the water comes out without any steam. However, continuing to flush will continue to lower the temperature of the brewing water. Perhaps the machine is operating normally, but you are greatly over flushing to arrive at such a low brewing water temperature.

Concerning the pressure, I don't know about the Oscar II, but the original Oscar didn't come with a vacuum breaker. So, you might try letting some steam out, then letting it warm up again for 10 minutes or so. This will relieve any "false pressure" and allow the boiler to heat normally. However, since you report being happy with the steam, this may not be the problem. I mention this because this issue has come up before. The pressurestat regulates the pressure of the boiler and, therefore, its temperature. See reference here ... am-tables/ While you may be happy with the amount of steam, this is not an indication that the boiler has reached operating temperature. Anything over boiling will produce at least some amount of steam, which you may judge to be adequate. Since the Oscar has no pressure gauge, I suggest you buy or borrow a multimeter that includes temperature measurement. It's a very useful instrument for troubleshooting and not particularly expensive. They usually come with a wire thermocouple. Alternatively, you may own a meat thermometer that has a remote probe. Put the thermocouple on the boiler and measure the temperature. If your boiler isn't insulated, it can help to cover the probe with a bit of rock wool to minimize variation due to the fact that the probe/thermocouple isn't in the boiler. Look up the temperature in the above reference and see what the pressure is. If it isn't at least 1 bar, then change the pressurestat.


#7: Post by jfuents »

I would try changing out the pressurestat to a Sirai model. If the unit is older the original part could be failing as this directly impact water temperature. Elektro's has a video on installing the pressurestat.