The group heads are not heating up on Nuova Simonelli 2 group.

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by CoruscatingCoffee »

I recently got my rebuilt 1995 Premier S to automatically turn off the water pump at start-up.
Now, I cannot get my group heads to warm up. The steam wands are steaming but my coffee is coming out barely warm.

The group head water release seems weak at start-up and sometimes the machine clicks into more water being released and sometimes it does not.
I can bang around on the heads with a rubber mallet and that seems to help, but I'm not sure of it.
It seems curious that both group heads are not warming up.
Are they both malfunctioning or is it a problem before the water gets to the groups?

I run a lot of water through the heads to get them close to a good temperature. Doing this lowers the pressure indicated on my pressure valve. The pressure drops out of the green zone into the blue. I wait until it heats up into the green zone again for the next shot.
I will try running more water through the group heads to heat them just before I draw a shot.
I've never had to do that before.
Why doesn't the boiler water get into the group heads to heat them up?
My portafilters don't even get hot.

Thanks for considering my problem.
"Make me one with everything" said the Zen Master to the hot dog vendor.

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Team HB

#2: Post by Jake_G »

Hey Frank,

It seems likely that you have some sort of scale buildup or other blockage keeping the water from flowing properly in your thermosyphon loops.

Strange that this just suddenly appeared on both groups. You say the machine is newly rebuilt and had teething problems with the pump running on startup, is that right?

Have you owned the machine for longer than just the startup period? What was done during the rebuild? While these are not always present, there should be a 4.0mm restrictor in the upper thermosyphon pipes to each group. These are a likely spot to catch any junk that may have been broken loose in the rebuild process, and slowing down the flow of hot water through the HX is about the only way you can have cold groups.

Best of luck,


- Jake

I found your old threads. It is "HIGHLY" probable that you broke some stuff loose that got caught in the restrictors of your thermosyphon when flushing the machine with descale solution. No good deed goes unpunished, they say.

Let me know if you need help identifying where to look. The restrictors should be threaded inside of the upper fittings that are threaded into the back of the groups.

The jet is item 7 here:
LMWDP #704

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CoruscatingCoffee (original poster)

#3: Post by CoruscatingCoffee (original poster) »

Jake, Thanks for your suggestions. They make such good sense to me.
I was given the machine by a barista who had it sitting in her shops' cellar for a few years. I rebuilt the machine myself in 2014 when I took apart every part and cleaned them individually. The only part I replaced at the time was the water pump, plus some pipes, gaskets, etc.

A couple of years ago I replaced the Gicar as water was pouring through my steam wands.
Last month I replaced the water pump again, when my group heads were not delivering water. I don't think that was the problem. I think you diagnosed the problem correctly. That's why banging on the group heads will often get the water flow to increase.

And a big thanks for sending the diagram with the blockage area marked. This will help me fix it right.

I'll let you know how I do,
"Make me one with everything" said the Zen Master to the hot dog vendor.

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CoruscatingCoffee (original poster)

#4: Post by CoruscatingCoffee (original poster) »

Well, a restrictor blockage was not the problem. The restrictor provided a clear 4mm passage through the larger collar. I checked one group head. I only need one group to function as I am the only person drinking coffee in the house.

The Nouva has some additional symptoms that may indicate another source of the heads not heating up. When I begin the pour, the machine noise is less and the extraction is slow. After many seconds, or when I bang on the head, the full power of the motor seems to kick in and the machine is noisier and the pour is stronger. At this time, some air also seems to be introduced into the pour. If I am near the end of the extraction, the portafilter starts releasing a bubbly mix of coffee foam. Could there be some air entering into the system due to a leaky pipe, gasket or connection?
"Make me one with everything" said the Zen Master to the hot dog vendor.

Team HB

#5: Post by JRising »

So perhaps the coffee circuit is leaking... Not air getting in, but steam displacing the liquid water.
The water in the coffee circuit sits there, slightly above boiling temp creating enough steam pressure to displace any water that is able to find its way out. There should be no place for the water to escape until the pressure exceeds 13 bar and forces past an expansion valve, or until the user opens the brew valve and lets it. Because the water is contained, it builds enough pressure to maintain a liquid state despite its temperature rising above the boiling point.
When you start your brew, the first couple of seconds are topping up the brew circuit, replacing the water that's been displaced before the pump can pressurize the system enough to start the flow through your portafilter. Additionally, with the brew circuit 3/4 full of liquid water and the top 1/4 full of steam, there's no thermosiphoning going on heating the heads... The heavy liquid water isn't going to flow uphill into the steamy part.

You'll have to find where the water is going. If you can't see it leaking externally into the body of the machine, it could be escaping backward over a check valve and making its way back toward the pump. If the pump outlet is hot while the machine's been idling for 20 minutes, then expect the check valve is leaking.
It could be a constant leakage over the expansion valve. This could probably be found by monitoring the flow in hoses after the machine has heated fully and is sitting idle. There should be no flow through the expansion valve when the brew circuit's fully heated & no longer thermally expanding.
It could be leaking over a close brew valve and dripping from its drain. This could be found by a difference in temperatures or noticeable drip.

The above thoughts are generic answers for machines that heat their heads by thermosiphoning. I don't know the Nuova Simonellis, please forgive the simplicity of the generic answer.

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CoruscatingCoffee (original poster)

#6: Post by CoruscatingCoffee (original poster) »

Thanks, John, for more suggestions. I'll try to get a handle on where steam and/or water problems are originating.
I'll mess with it tomorrow to see if I can trace the problems back to something I can fix or replace.
"Make me one with everything" said the Zen Master to the hot dog vendor.

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CoruscatingCoffee (original poster)

#7: Post by CoruscatingCoffee (original poster) »

I have been searching for my fix on the wrong side of the Nuova. I couldn't see the back of my machine because it was up against the wall.

I finally pulled my whole table away from the wall and found the steam leak on the tank end of the connector pipe. That is the pipe that I just checked per Jake's suggestion. He was right. I was looking at the group-head end of the pipe instead of the tank end.

Thanks Jake and John for helping me to this point. I hope I can seal the steam leaking connector that is coming off the top of the tank. It may take more than thread seal tape to do it. Can I use Loctite on a fixture coming out of the boiler tank?
"Make me one with everything" said the Zen Master to the hot dog vendor.

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CoruscatingCoffee (original poster)

#8: Post by CoruscatingCoffee (original poster) »

Problem solved.
I managed to seal the high pressure steam leak with Loctite Blue. I used pipe sealing tape first. That did not work so well. If the connection at the boiler starts leaking again, I'll try Loctite Red.
Thanks again to this forum's helpful participants.
"Make me one with everything" said the Zen Master to the hot dog vendor.