Bob, there are two parallel issues going on here: 1) your now-dead water heater and 2) your ground sourced heat pump system that uses groundwater as your thermal sink for the heat exchanger. The ground source heat pump potential for scaling will depend somewhat on how the system is configured (two wells for an open loop, water exchange back into the same well, water discharge to some other place?). Regardless, of the configuration the two potential issues are scaling your lines and clogging your well screen and/or sandpack. The pipes you should be able to assess by popping them open at a joint or two and looking. Pretty straightforward. The well can be trickier in all regards and the issues there could not be visible in the above ground piping. Depending on the well construction and appurtances, you may be able to use measurements of drawdown relative to flow rate (Specific Yield) to track well efficiency through time, of you can rent a video camera. Should you have clogging in the well screen, well rehab amounts to pulling pump and using mechanical and/or chemical approaches to break up the scale or bacterial fouling, neither of which is a sure fix. If you are indeed in a karst area and your well just stubs into an underground cave somewhere, the well efficiency isn't like to be an issue, but there could be other things to keep you up at night... like sinkholes.