I need to know the stock gasket arrangement for the GS/3 steam boiler level probe. Is it just a single copper washer, or is it a copper washer plus a fiber gasket? The diagrams in all of the versions of the parts manual show only a copper washer. But when I look at the fitting, there's some other substance between the copper washer and the fitting.

I took these pictures when I removed the probe for inspection a couple of years ago:





At the time, there was a layer of hard brown stuff over the white substance you see in the photos (you can see a bit of it around the edges. It was flaking, so I assumed it was the remnants of a fiber washer and scraped the rest of it off. That revealed the white stuff. It has the consistence of plaster -- if I scrape the surface, powder comes off. I can't tell if this is some sort of filler that's been poured into a recess in the fitting to form a seal or if it's the remnants of a fiber gasket -- i.e., calcium deposits from water that soaked into the fiber gasket before it disintegrated. I was afraid to dig down into the white area, so I left it as is. I can't recall if I installed a new copper washer, but the fitting sealed OK when I reinstalled it.

Then the other day I heard the sound of steam coming from inside the GS/3 and discovered a very small leak coming from the outer fitting of the steam boiler level probe. The leak is so small that steam isn't condensing inside the machine -- yet. In fact, I had to use a rubber tube as a kind of stethoscope to listen to each fitting until I could hear the steam escaping. But I found the source.

I tried tightening the fitting, but that increased the sound of the leak. So I turned off the machine, let the pressure out through the steam wand, and removed the probe. The copper washer looked pretty worn, so I replaced it. I found the same brown gunk underneath it that I had found before, and scraped it off until I saw the white stuff again. And once again I wasn't sure if I should remove that stuff. Unfortunately, when I re-installed the probe, the leak was a little worse.

The only steam boiler probe sold by espressoparts.com, which has a different part number and a longer straight probe, has the same fitting. On the same page they show a fiber gasket intended for use with that probe.

So, I'm wondering if all I need is a new fiber gasket, or if that white stuff is some sort of filler and I need to replace the entire probe assembly.

Does anyone know?

Replying to my own post, the service manager at Chris Coffee told me that the white stuff is probably the remnants of liquid sealant the factory sometimes uses to seal fittings. He advised scraping it off and wrapping the fitting with Teflon tape. He said that's safe even for steam boiler temperatures and that's what they do.

We shall see...

Assuming this fitting has a recess as you describe, a copper washer (alone) would be hard pressed to effect a good seal.

Teflon tape was obviously not used during the original build but I certainly agree that it would work in this case.

If it were me, I would order a new fitting and several fiber washers as a "spare".

I went with the Teflon tape and it worked.

First I scraped off/out all the white stuff. Turns out there is indeed a recess or channel in the fitting, which was filled with this hard white material. The material had cracked and flaked enough to prevent a good seal with the copper washer, so it had to dug out.

BSPP fittings are designed to seal one of two ways: with an O-ring or with a washer. The threads are not supposed to be sealed. The idea is that you can screw the fitting all the way in, and the O-ring or washer will seal the connection. I have some BSPP fittings with O-rings, and in all cases the fitting has no channel and the O-ring is inside a washer. I believe the washer is there to keep the O-ring in place and prevent squashing the O-ring too much by over-tightening.

I believe the level probe fitting, which is a 1/4-1/8 reducing bushing, is actually designed to be used with an O-ring. The O-rings from my BSPP fittings fit perfectly in the recess. But I think it's supposed to be used with just an O-ring, no washer, with the channel holding the O-ring in place. LM may not have opted for an O-ring because the standard O-rings that come with BSPP fittings are rated 212F or less. Not sure why they wouldn't have substituted a Viton O-ring, but maybe it wouldn't hold up over time in that particular configuration, or perhaps it would be too easy to turn the nut when tightening the probe positioning nut.

BTW, the GS/3 parts catalog says the level probe part number is LA052, which I can't find online anywhere, but the Italian column shows part number TL10/B. Googled that and found it's also a part in the GB5/FB80 series.

Anyway, there's no doubt the recess was deliberately filled in order to make the fitting work like a BSPP with a washer seal (a copper washer is specified in the parts manual.) It's a mystery to me why they did this. I guess it's possible they couldn't find any bushings without a recess, but that seems hard to believe.

I briefly considered using one of my O-rings, but the temperature rating was just too low to consider going that way. I could have used sealing paste, maybe trying to fill in the recess, but that didn't seem like a very good idea and probably would have been messy. And I couldn't find my tube of paste anyway.

So, in the end I wrapped the threads with Teflon tape. I went all the way down to and into the recess with it, and I used more wraps that I normally do. BSPP fittings aren't like NPT fittings -- i.e., they don't bunch up the tape as you screw in the fitting.

I also used a different copper washer. I had some stock LM 1/4" copper washers for use with the vacuum breaker valve upgrade, but they have burrs and don't look all that flat. I had bought a bunch of washers from a real good fitting vendor, and they seemed to be much better quality -- flat, no burrs. So I used one. It's a tad smaller OD than the LM washer, but that might be a good thing. There's a recess at the opening of the boiler that it fits perfectly.

Ran the machine for several hours and heard not a peep from the fitting. If it leaks again soon, I'll replace the probe. Probably a special order from LM -- can't find it online.

One thing I noticed while inside the machine: every AC connection has an insulator over the female spade connector, and they've all dried out to the point where if you touch them they crack and fall apart. Does anyone know of "snap together" lug insulators that could be added without replacing the female spade connectors?

Most fittings that go directly on a boiler use copper crush washers to seal. The heat from the boiler would break down an O ring unless it was specifically made for high temperatures.

Yeah, that was my reasoning for not going with an O-ring, even one made for high temperatures.

This leaves the mystery of why LM used a bushing designed for use with an O-ring, then filled in the channel to make it work like a fitting designed to be used with a washer.

My speculation is that their selection of bushings was limited by the requirements of running the temperature probe through the fitting. First, the bushing has to convert 1/8" female to 1/4" male. Second, the exit hole at the 1/4" end has to be exactly the diameter of the teflon insulating sleeve in order to ensure a steam-tight seal between the sleeve and the fitting. Finally, when the 1/8" bushing is screwed in, the teflon sleeve has to be compressed enough to fix the position of the probe and form a steam-tight seal around the probe.

That last part has me wondering. It's not at all clear to me how or why the Teflon sleeve compresses when you screw in the 1/8" bushing. I believe a BSPP bushing would just screw all the way into the outer bushing without compressing the sleeve. The fact that the inner bushing can't be screwed in all the way leads me to speculate that it has tapered threads -- i.e., BSPT or NPT. That would require the outer fitting to convert between thread types, yet another constraint on choice of outer bushing.

That said, I still don't see how even a tapered fitting would compress the Teflon sleeve. Actually, tightening the inner bushing makes the probe harder to move, but you can still move it with moderate force. And that makes me wonder how the heck the seal can be steam tight!

Peppersass wrote: One thing I noticed while inside the machine: every AC connection has an insulator over the female spade connector, and they've all dried out to the point where if you touch them they crack and fall apart. Does anyone know of "snap together" lug insulators that could be added without replacing the female spade connectors?

Why not just replace the insulators with heat shrink tubing?

Well, that would be better than nothing, and I have plenty of the stuff on hand, but I'm not wild about using heat shrink alone to insulate AC connectors or splices. It's fairly thin and subject to puncture by the sharp metal edges of the connector. At a minimum, I'd probably want to put a layer of electrical tape on the connector first, and then it will probably take some care to position the heat shrink so that no metal is exposed after shrinking it.

Also, I haven't checked this yet, but sometimes the connector depth is shallower than the lug length and allows a small bit of the lug to remain exposed. The stock plastic insulators extend to cover that.

These are the reasons I'd prefer a thicker, snap-on insulator designed for the purpose -- if available. If not, heat shrink is a good fall back.

Buy some good quality tubing & your connector won't poke through. I've been using it on connectors for over 35 years without issue. It stands up to heat much better then the slip on covers typically used inside espresso machines.

The white stuff you found is a fiber washer that is used for sealing. LM used only this for many years, then went to the copper washer. The probe comes from Gicar and is a standard part that come with this white fiber washer. Current production uses the same probe with the fiber washer (because this is how it is sold) and a copper crush washer, no PTFE tape (but maybe some liquid sealant on the threads).


BillC