Nuova Simonelli Oscar - leak at upper HX connection to group head

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GeoTomCC

#1: Post by GeoTomCC »

My ~2010 Oscar was leaking from above the group head. As I'd thought, there were cracks in the top side of the group head (2 are cracks above the inner and outer edges of the thinnest part of the group head) and I ordered a replacement one from eReplacement Parts. Has anyone else experienced a cracked group head?

I've installed the new group head, but there's a leak at the connection of the HX pipe to the top rear threaded stem of the group head. I've tried multiple times to adjust the positioning of the nipple at the end of the HX pipe relative to the threaded stem and have tightened the connection as tightly as I dare, but it still leaks badly. Has anyone else had this problem and, if so, any solutions?

The concave socket at the center of the threaded stem of the old group head seems to be just a little deeper/wider than the new one. I'm hypothesizing that: 1 - the seal between the nipple and the stem is where the wider flange at the rear of the nipple is pressed tightly against the 'face' of threaded stem, and that, 2 - the apparently narrower/shallower center of the stem on the new group head is pushing against the 'dome' of the nipple and isn't allowing the flange on the back side of the nipple to completely seat against the 'face' of the threaded stem. I've taken a conical Dremel grinding bit and by hand (not using the actual Dremel tool) have reamed out the center of the new threaded stem just a little bit, in hopes that the nipple will be able to better seat against the threaded stem. Since I had the machine opened up, I've taken the opportunity to address other issues, like replacing the tank insulation and the water retention valve (which had clearly failed and strewn white and green plastic parts and a small metal spring through the hydraulic system) and am awaiting parts to complete those repairs. Consequently, I haven't gotten back to testing the HX connection to slightly modified stem on the new group head.

I'm really interested to hear if others have had this problem, and wanted to also alert others replacing their Oscar group head to this potential problem.

Oh, I'm new to the Home-Barista site and this is my first posting, so forgive me if I've done anything incorrectly (and let me know, please).

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cafeIKE
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#2: Post by cafeIKE »

If I ever take a group off, I loosen the boiler mounts, tighten the TS lines before I snug up the group and boiler.

Photos, cropped if you can, are often helpful.

vas

#3: Post by vas »

GeoTomCC wrote:I've tried multiple times to adjust the positioning of the nipple at the end of the HX pipe relative to the threaded stem and have tightened the connection as tightly as I dare, but it still leaks badly.
If it leaks badly then it's unlikely something on the contacting surface. When you disconnect the tube from the boiler, does it move? Maybe the thread has problems and the nut doesn't press the flare in properly. I'd also check for a crack on the flare an the pipe, and the brazing joint between them.

GeoTomCC (original poster)

#4: Post by GeoTomCC (original poster) »




Well, I decided to do a more thorough tear down of my Oscar, descale the tank/HX and replace the decayed tank insulation with some hi-temp silicone insulation (orange material in photos). I put everything back together and turned on the machine. After the pump filled up the tank I punched the brew button to trigger water flow to the group head before the machine had heated up (figured the machine didn't need to be hot to test for the leak). As you can see in photos, there's still a major leak at the connection of the top HX tube to the group head. The blurry pic shows the leakage better, but it's still evident in the sharper pic. In both cases, the leakage is from the front of the compression nut, not at all from the rear.

I was unable to detach the top tube from the tank - it just wouldn't come loose (I'd had a bad prior experience trying to force the issue with a tank fitting and I didn't want to repeat that mistake. However, when I had the tank removed from the machine I able to get a pretty good look the the top tube and the brazed-on nipple that connects with the threaded stem of the group head, but couldn't find any evidence of a crack or a bad braze. The compression nut turns appropriately and I can't see or feel any indication of damaged threads.

NOTE: has anyone else noted that the exploded diagrams on various on-line parts vendors (e.g., Espresso Parts, eReplacement) websites show the top tube, but it's not listed in the parts list as an available part for purchase.

When I replaced the group head, I also replaced the 3-way solenoid valve, figuring it would be a good idea to go ahead and do both at the same time. If the new 3-way valve isn't opening correctly, might that produce an over-pressure situation prompting the leak? (I wouldn't think so).

Anyhow, I'm really at a loss and about ready to call the local espresso machine repair business to see if they can fix it.

Thanks in advance for any ideas,
Tom

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cafeIKE
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#5: Post by cafeIKE »

I'd surmise corroded surfaces

vas

#6: Post by vas »

GeoTomCC wrote:In both cases, the leakage is from the front of the compression nut, not at all from the rear.
If it leaks from the front of the nut it either is a bad contact between the nut an the group, or it might very well be a crack in the thread of the group. When you tighten it up it becomes wider and let the water through.
GeoTomCC wrote:NOTE: has anyone else noted that the exploded diagrams on various on-line parts vendors (e.g., Espresso Parts, eReplacement) websites show the top tube, but it's not listed in the parts list as an available part for purchase.
PartsTown has the tube available for purchase.

GeoTomCC (original poster)

#7: Post by GeoTomCC (original poster) »

Boy, I haven't seen any evidence of a crack in the threaded stem of the new group head. Also, no signs of corrosion on the new group head (it's brand new), or on the top tube nipple where it connects to the group head.

I'm thinking, now, of reinstalling the old, cracked group head to see if there's leakage at the top tube-group head connection (it will, of course, leak from the cracks at the top of the group head). If there's no leakage at the connection, then there's something awry with the new group head, right? If I do this, I'll check the threaded stem of the group head, again, for cracks/irregularities.

CafeIKE: Sorry, what are "TS lines"?

vas: I do think the problem is that the nipple, for a reason not clear to me, isn't properly seating with the threaded stem of the group head. Also, thanks for the info re: availability of the top tube at PartsTown!

Thanks to everyone for your thoughts and suggestions,
T

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cafeIKE
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#8: Post by cafeIKE »

GeoTomCC wrote:CafeIKE: Sorry, what are "TS lines"?
TS: ThermoSyphon.

It's my feeling that having a bit of play in the alignment when tightening the fittings gets a better fit than trying to force a pipe into a rigidly immobile seat.

GeoTomCC (original poster)

#9: Post by GeoTomCC (original poster) »

I'm pretty sure that I've solved the leak problem.
Removed the new group head and the threads near the base of the threaded stem are damaged, or weren't machined properly (the later, I think). The compression nuts spins on properly and tightens, but the bad threads at/near the base of the stem look to be preventing the nut from tightening all the way. I re-installed the old, cracked group head, and no leak. So, that confirms a problem with the new group head. I've ordered an M14-1.5 die, which by my measurement looks to be the right size, for cleaning up the threads. Hope that works. Alternatively, I could send the head back to eReplacements, but I'm wary of all the paperwork, delay and hassle that would entail.
T

GeoTomCC (original poster)

#10: Post by GeoTomCC (original poster) »

Well, I was wrong, again. I cleaned-up the threads of the group head stem with the appropriate tool die (M14, 1.5mm pitch), reconnected everything, and still a big leak at the connection of the boiler tube to the group head. Since there was no leak when at the connection when I re-installed the old, damaged group head, I figured there must be something about the new group head that doesn't mate properly with the boiler tube connection. So, I ordered another new group head, this time directly from Nuova Simonelli, and installed it 2 days ago. Aggh, no difference! Once again, the connection leaked horribly.

So, I've now ordered a new boiler tube from PartsTown - it's out of stock and is gonna take 10 days or so to ship.

My wife is pretty tired of all of the disassembled Oscar parts littering our dining room table. Can't blame her, so am I.

I've avoided removing the boiler tube until now 'cause I couldn't get it to release from the boiler with a reasonable amount of force. Any tips on the best way to get it to release?