I was getting some sputtering sounds (like water on a hot skillet) and intermittent steam hissing sounds.
The emergency pressure vent on the steam boiler was not sealing properly. This is the big tall brass valve with the plastic cover, between the two heater coil terminals on top of the boiler. You could clearly see steam condensing on the inner surface of the plastic shield where the valve exhaust ports are. (You have to take off the side panels and the back to really see this)
I removed the valve, took it apart (unscrewed the top) to examine. The brass seat on the lower half of the valve was uneven. We lapped it smooth with a diamond abrasive plate. Also, we took apart and inverted the white teflon seat washer on the poppet part of the valve, as it was a bit worn and scratched.
We reassembled the valve and added about two extra turns of spring preload (screwed the top half on two threads further than it was originally) There is also a locknut you must tighen against the top half of the valve.
So far (two days) I'd say the problem is improved, but not 100% solved. It looks like the seat in the lower half may not be at right angles to the vertical axis.
Also, while in there I checked the connections to the heater terminals. One was loose and the extra resistance/heat had discolored the crimp terminal and melted some of the insulation on the wire, and also part of the plastic boot cover. I pulled it off and tightened it a bit with pliers, then put it back on.
More of that fine Italian craftsmanship...
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