So, I am back with my expobar lever machine. I had problems with this last year, and in 2009, and in 2007. At least. :O

I was cleaning it a bit before making espresso today. I used the hot water outlet to fill my pitcher
about 1/4 way with boiling water to clean my portafilter. I cleaned it and about a half hour later
I pulled a shot. Everything seemed ok. After this, I started to froth milk and was a little distracted.
I could hear the steam pressure going down, I looked over at the gauge and it read zero and the heating
indicator (red light) was on. I stopped frothing and noted that the red light was still on, and the
pressure then started going up... really really fast. Before I could even reach the off switch my breaker
on that circuit tripped.

I let the machine totally cool. I then reset my circuit breaker and plugged it in. The pump started running.
I shut it off after about 45 seconds. (I did not want to let it run too much). I noted that the water
in my reservoir was going down, so I did that again (turn it on, pump starts, wait 45 seconds turn off).
The third time was the charm, and the pump stopped. The heating element is not coming on now.
The red light on the right of the machine does not light.

tl;dr, I think I ran it dry and now I think the boiler heating element is not getting juice.

So, I took it apart and checked the boiler heating element itself with no connections. I get 13.2ohms. Not sure if that is correct. I checked across the pressure stat and I have a dead short 0.0ohms. Not sure where to go from here... but we have no coffee machine other than this one!! :O Any help would be appreciated.

Is there an over temperature cutout?
Some machines have a resettable one, that looks like a squat cylinder, maybe 1/2-3/4" diameter with a red button in the middle. Some have a non-resettable one wired in, sometimes hidden inside a sheath.

Since you seem to have a multimeter, trace the wires, looking for any open circuits.

Ok, Ok, I DID find a resettable circuit breaker on the temp sensor in the unit...
man that thing is small.

So, now it is working again. I may need to start a new thread for this, but if not here goes:

I still can not figure out why it keeps doing this... e.g. when I use the hot water from
the boiler, it sure seems like the pump will NOT run after until I turn the unit off and
let it cool. Secondly, my espresso is now very bitter, although the pressure seems correct.

Thank you so much for the help on this... The local coffee shop is all the way
across town and not so great.

You said the pump won't run to fill the boiler? Maybe try removing and cleaning the boiler water level sensor.