Espresso machine operational again

Since Silvia asked me for an update, here it is: I fixed the boiler problems on my espresso machine. Fixed is a pretty misleading word, actually. I turned it off, let it cool, removed the vacuum breaker valve and saw that the boiler was overly full. This means that the water level sensor wasn’t telling the pump relay when to stop filling properly.
To “fix” it, I drained the boiler back down to 3/4 full (the top quarter is for steam), jiggled the water level sensor (this may have dislodged a piece of grit or something), put the vacuum breaker back, and fired it up. Behold, it works!