If you're never had to deal with it before, then it was no O ring, unless it was some special material.
O rings are original on mine. I bought a bag of a hundred plain old Buna ones for about a nickel a piece. Every 9 to 12 months or so there's a little dripping that starts to happen. I remove the ring around the toggle, pull out the valve assembly, and pop a new one on the tip. A little silicone grease, and it's done.
I think I've replaced the O rings on the body of the assembly only once. It's the one on the tip that opens and closes the steam access that sees most of the action.

I got the usual fast service from Stefano.

Nice kit w/ a chart showing where stuff goes.



The business end of the valve piston does have a funky seal. Perhaps an o-ring would work, but the version Stefano supplied looks more like the one that was deteriorated in my valve.
Front (valve seat) side:

Back (piston) side:

My machine was not equipped with that fancy seal! I feel deprived!

It sure lasted a long time. Plus, you can count on Stefano to have the best.

More surgery this weekend on the Mondiale.......

The 2-way solenoid between the pump and the boiler took a dump. Fortunately the flood wasn't much and the GFCI squelched further damage. Stefano gave me some quick action with a new Parker valve and I'm back in bizznezz. Put in a new Anti-Vacuum Valve while I was in there. All good now and excited to see what the Mondiale will do with CCC's Banko Gotiti Natural Sundried as an Americano tomorrow morning.

My sad run of unanticipated maintenance on my aging Isomac Mondiale continues. The Crouzet SSR died this Saturday. Fortunately it was after company went home,......but Sunday morning ...... I was not a happy man!. In order to remove the SSR, you first gotta remove the Procon Pump and Motor which fills the back half of the chassis. I'm figuring that if I'm gonna go to all of that trouble, I might as well relocate it to under the bench. The new SSR and the Giemme Control Box will be relocated on aluminum risers at the back of the Chassis instead of directly under the boiler. I have always thought it was damn silly to have electronics under a water reservoir that might potentially leak. 2-ways valves fail-n-leak, Anti-Vacuum Valves send up a short fountain of water everytime the machine gets turned on, etc, etc. I popped open the dead-beat SSR...and you guessed it, water corrosion! ....well hopefully no more!

I bolted the motor frame to a 2x12 board using rubber insulators and then screwed the board to the cabinet. It should be plenty sturdy. Wiring and plumbing are not complete yet.





Oh yeah...since I'm in there, I'm also replacing the Siria pressurestat. Responsiveness hasn't been very good recently, and ......Dan, sez I'm pushing the envelope using the original ~10 year old pressurestat

I pulled the cover off of the controller and everything inside looks clean....so I'm hopeful that I can get a few more years out of it....pricey little rascal. At least I should be able to get at it easily in the future now that the pumps is out of the way.

I'm currently stalled until I get some parts from Stefano, but hopefully this exercise will be beneficial:
- lower noise from the pump......might relocate the 2-way valve also
- moving the electronics away from water

New parts arrived from Stefano and now installed. Very pleased with the result. Now I won't NEED to buy that LM GS3 for a little while. I finished late in the eve, so no pictures of the interior and it looks the same on the outside as earlier in this thread.

Parts list:
Item - Pressurestat SIRAI 30A
Item - Temperature Insulation Sleeve
Item - Female Spade Connector
Item - Male Spade Connector
Item - Female Spade Connector Cover
Item - Male Spade Connector Cover
Item - Isomac SSR Relay
Item - Heat Sink Grease (Thermal Paste)
Item - Isomac Red Light 115v
Item - La Pavoni Power Cord Grommet
Item - Isomac Control Box Protection
Item - White Wire 14AWG 600v 150c
Item - Stainless Steel Braided Hose 3/8 BSP 150cm
Item - Green/Yellow Wire 16AWG 600v 105c
Item - Black Wire 16AWG 600v 105c
Item - Blue Wire 16AWG 600v 105c
Item - NEW Anti-Vacuum Valve with Barbed Fitting
Item - Silicone Hose 6x9mm
Item - Copper Gasket for the anti-vacuum valve
Item - Copper tubing to re-run some interior plumbing lines
Item - various plumbing fittings / adapters

My 3 favorite things about this latest maintenance project:
1 - Moving the pump out of the chassis and off of the counter is awesome for sound and interior space. I could fit another boiler in there now...hey wait a min.......naw, that's a silly idea, Id rather have the GS3.
2 - The new pressure stat has a nice narrow dead band and is accordingly FAST...way faster than my old 10 year old one.....and is more responsive to tuning. If you are running a SIRAI that is more than 7 year old, think about a rebuild or a replacement...I'm loving it now.
3 - The barbed anti-vacuum valve keeps the interior nice and dry as it dumps the spittle to the drip tray via the front vent instead of the top of the boiler.

I'm gonna play with some additional sound deading ideas as I still have more hum than I want....there is always something.

Glad to hear that you gave new life to your Mondiale! It has historical significance to this site. You of course know this, but for HB trivia fans, the site's About Home-Barista.com explains.

The score has turned out well for both of us. Thanks!!

She still has very appealing looks as well as conduct ,.....especially now that she's got some new innards.

My experience, FWIW, with my Relax is that it went through a critical period (about 6-8 years old) where I was replacing parts with surprising regularity. It is now at 10 years and the replacement has slowed down. Nevertheless, I maintain a parts inventory. The red & green lights always seem to break when I'm doing maintenance so I have those in stock. I have replaced the controller box (relays stuck), SSR (although it didn't need it so I have a spare now), heating element x 5 (there was a period where I was burning it out during descaling, my error), pressurestat, steam gauge pipe (arced a line voltage wire across it), pipe from boiler to group, the boiler (!), OPV, brew valve o-rings, and probably a few things I have not thought of.

Stefano is a godsend for parts and advice, on top of being a really nice guy in person as well.

When the boiler developed a leak, I was very seriously considering junking the Relax. A new (stainless steel)replacement was about $500, and I really thought I'd rather invest it in a new machine. I found a used boiler and that brought the Relax back to life. With continued replacements, I would expect to get another 10 years out of it. But, like you, the GS3 sirens call my name. Sigh.

Very cool Dana. Maybe when we are ready for the next Isomac "rebuild", the GS3s will be available on the used market and we will be able to reapply our skills at a kinder price point.