Used Mini Vivaldi 2 with various issues

[Enginerd]

I purchased a 10 year old used Mini Vivaldi 2 recently with a known issue (I did purchase at a deep discount to offset the risks). It came with a 15A/20A converter. I planned to use it with the converter as I don't have the 20A outlet. The 15/20A switch does not have a label but it's set to the position that typically is 15A mode

The prior owner claimed that the steam boiler has a runaway pressure issue. The pressure goes into the red and the emergency relief valve is activated. The following is an account of what I have observed since bringing the machine home. I am hoping I can get some tips on next steps based on my observations and findings. For context, I have tinkered with electronics since I was a teenager and I have a couple of degrees in electrical and computer engineering. Having said that most of my current work is abstracted far away from electricals and electronics so I am rusty. But feel free to get as technical as you'd like.

1. When I brought it home, I hooked it up to a GFCI outlet in the garage. It turned on with the ON/STANDBY light flashing. So I proceeded to press the hot water and ON/OFF button simultaneously. The water came out the grouphead for a while. I let go of the buttons and may have done the procedure one more time. I let go of the buttons.. At this point, I noticed that the steam pressure was rising rapidly. As soon as it went into the red, I pulled the plug out.

2. This matched what the prior owner had said but I had expected more time for the pressure to rise. Also my understanding is that the brew boiler should reach temp first and then the steam boiler. So once the machine diffused the excess pressure, I removed the vacuum breaker and inspected the inside. I noticed that there was no water in the steam boiler. That felt odd. I was tempted to funnel water into it but I chose not to. I closed up the vacuum breaker and tried the sequence one more time to run water through using the ON/OFF + hot water button. Same result, and I couldn't tell if water was making its way into the steam boiler. So I stopped it immediately.

3. The next day I plugged the machine into the outlet and it wouldn't turn on. This was odd. It hadn't done it the last 2 times I had plugged the machine in. I didn't realize it had tripped the GFCI protection. I tried a different outlet without realizing it was not protected and saw an arc and explosion in the machine. It felt like a fuse blew up or something (so there's possibly another issue now and I realized that I was not being careful). But the machine did turn on. I switched back to the GFCI circuit and it tripped again.

4. So I decided to trouble shoot this ground fault. I opened the steam boiler circuit by disconnecting the probes as well as the connection to the high limit switch. This stopped the GFCI from tripping. I measured the resistance across the probes and it's at 9.7 ohms. However, when I measure from the probe to the boiler body, I get a finite reading in the 20K ohm range. The meter doesn't immediately settle on that value; it also does not trip the continuity test.

5. Today I did turn the unit on without the boiler connected electrically. And then I pressed the ON/OFF switch. The pump turned on and I heard water filling up. My guess is that the boiler filled up with water since the brewing boiler was already primed. I saw the brew pressure needle vibrate while the pump was on. The brew boiler heats up just fine.

So where do I begin to try and get things working completely on this machine? My guess is that I should have the ground fault resolved first. From what I have read, the boiler heating element may be causing the electrical leak and most likely the boiler needs to be replaced. Could it be anything else? Is there anything else I can do to narrow down the issues in this machine?

Thanks in advance.

[Enginerd]

Since my post I opened the vacuum breaker and do see that the boiler is filled with water now. This means that upon starting the first time, the boiler may have tried to heat up dry. As far as my understanding goes, that shouldn't have happened. Perhaps that initial cycle of dry heat my have created the ground fault. =/