The (old and clunky Sirai) pressurestat on my CMA lever has been leaking a small bit of steam since I first rebuilt it; at this point, it seems to leak a little blurble of water when it clicks off.

Either because of the steam, or independent of it, it is now failing in an interesting fashion.

I noticed that the pressure was hovering around 1.0 bar, but didn't seem to be making it to 1.2 bar. Usually I get a swing from 0.8 to 1.2 or so. I could hear the heating element kicking in (noises from the boiler) and off, but no click from the pressurestat. How odd. After diagnosing back the chain with a voltmeter, I isolated the problem at the pressurestat, and surmise that one of the connections (I'm guessing the middle of the three) is corroded and acting as its own switch, letting the boiler pulse on and off independent of the pressurestat/pressure, and just happening to keep the boiler at around 1.0 bar.

I killed the power and opened up the pressurestat, and clacked the contacts against each other a few times. It seemed a little better behaved after that. I may switch that position to the unused contact, which should hold me until I get a replacement pressurestat.

Allon: So how did switching from one set of contacts to the other go? From what you were describing your heating element might not of had full voltage due to high contact resistance in the pressurestat. That would/could cause it to run at a lower wattage and not fully heat the boiler. The energy expended in trying to get through a bad contact would also result in heat at the point of resistance causing the problem to make itself worse. If the other contacts are in good shape and making good contact (not keep from tight contact by the bad set) that should keep your machine running.
Duke

duke-one wrote:Allon: So how did switching from one set of contacts to the other go?

Well, my first thought was to replace it with another Sirai from a friend's espresso machine that I'm currently rebuilding...however that one has two scorched contacts as well....

I burnished the contacts with a little fine sandpaper - not a great idea - I know I should use a burnishing tool, but I don't have one handy and I plan on replacing the pressurestat soon anyway, as soon as I finish putting together my OE order...

I moved one set of leads to a previously unused contact, and the other is one one that I cleaned up a little bit. We'll see how it goes. I have the machine heating now. Maybe I'll have espresso in the morning (I won't leave it on overnight). At least if the bad contact sticks, the good contact should still break, and I left the cover off of the pressurestat so I can visually inspect it, and so that the steam leak doesn't make the insides moist.