What is model on the heat pump?
Do you have gauges to check refrigerant pressures to verify compressor is actually pumping?
Either compressor is not pumping the refrigerant or there is something preventing flow of refrigerant from making it's cycle
Compressor pumps the refrigerant to the exchanger and back .Each time refrigerant goes across exchanger, heat is removed and heats the water then it returns to compressor and starts over. Sounds like something is not opening to allow the refrigerant to flow, so cutting off on high head pressure.
.The compressor is the pump. It compresses refrigerant and pumps it to the exchanger and back.
2.Looking at the manual on the unit,. it does appear to have an electronic expansion valve
The expansion valve is what opens and closes to meter the amount of refrigerant to the exchanger .If that expansion valve does not open, refrigerant can not get though to exchanger.
3. If board or expansion valve either one was damaged could be the issue. Have you replaced the board already?
I think I would obtain gauges so you can see what is going on.
As for manual I am sending a link to what I have.
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THanks for the update. You are correct about the power company. I have heard of this creating an issue even with single phase equipment when they replace transformers.
Your compressor was actually pumping backwards