Whoa! That's a lot. What could make a one stick? Corrosion? Being stored in a damp environment?
What is that machine anyway?
One simpleton and an unfortunate confluence of events, most likely. The pressure stat diaphragm leaks, ancient bi-metallic safety tstats fail to open, boiler pressure rises, popoff valve releases steam, some idiot removes the popoff's safety seal and tightens the valve, and eventually enough pressure builds until the boiler ruptures.
BOOM!See, it's pretty simple to turn a safe espresso machine into an IED.