I'm new to the site and my knowledge of HVAC is very limited, almost non-existent before this recent incident so I'll try to give as much background info as I can. A few days ago I received a call from the housekeeper saying there was water coming from everywhere. I rushed home to find water pouring out of the walls and ceiling. After we got the water turned off and cleaned up, I started looking around to find the source. Turns out that the DHW input line on my WFI geothermal unit ruptured at the Pex/copper line junction. There was about 2ft of copper coming out from the front of the unit and then pex the rest of the way. After making some calls, my installer told me that they now recommend at least 5ft of copper on the unit side. I assumed the desuperheater line just got too hot and ruptured. As I looked more in depth to the system, I noticed that the desuperheater loop was plumbed incorrectly. Instead of DHW IN teeing into the cold water input of my hot water heater and DHW OUT going to the boiler drain, DHW IN was teed to a random domestic cold water line and DHW OUT was piped directly to the cold input of my HW Heater (making it the only input source for my HW heater). Even I, with my VERY limited knowledge of HVAC realized this was incorrect. Its not even a loop and really only works as a pre-heater if the HW heater is being drained frequently. As this is a vacation home, the HW heater very seldom gets used and the heated water from the desuperheater just sits in the line.(to my understanding). I checked the other four units we have on the property and they are all plumbed the same way. After the units dried out, our HVAC guys turned the affected unit back on and it would only run for 2 or 3 mins at a time. After some diagnostics, they found a problem with the TXV. To my understanding that is a metering device that controls the flow of liquid refrigerant. OK, now for the questions...

1. Did the incorrect plumbing of the desuperheater and the lack of use of the HW heater cause the temperature in the desuperheater lines to become to high and make the pipe rupture.

2. Had we had 5ft of copper installed on the DHW in and out lines, would the heat have dissapated enough to cause the line not to have ruptured.

3. I've been led to believe that TXVs don't malfunction very often, but assuming it did, could it have caused enough heat buildup to cause the pipe to rupture.
---(I know more heat can be created by them causing the unit to run for extended periods, but our unit seemed to only kick on for 2-3 mins and then off for several minutes)

4. Could the unit being doused with that amount of water (I removed upwards of 300 gallons from the house) have caused the TXV to fail.

I feel that improper plumbing is the main cause of this issue, but my HVAC knowledge is very limited. Regardless of what caused the problem I need to have all of the desuperheaters re-plumbed correctly, but y'all know how it is when something goes wrong. Everyone is trying to pass the blame. My main objective is to get the original plumbing contractor to cover the re-install, and I need a little info in case I have to get ugly with them. In my opinion they installed something incorrectly and they need to make it right. Our HVAC contractors are stand up guys and if I have to threaten the plumbing company with enlightening our homeowners insurance about the incorrect plumbing I want to make sure it doesn't get tossed back in our HVAC contractor's lap.

Thanks in advance for any information y'all can pass my way,

ps. sorry for such a long post, I just don't know enough to be any more concise.