Since they are essentially the same in principle the geothermal heat pump is about as reliable (or unreliable) as standard air conditioning unit. The extra expense for ground/pond loop is paid by energy saving. We used to have standard forced air furnace in my former house. I was changing the igniter about every other year, fan motor once, refrigerant leak once, thermostat once and few more issues I don't remember. All in about 9 years. We have geothermal in our new house for past 5 years and so far didn't have to replace anything except one pump that was too small for the load. I spent about 500 USD on new control system but it was more or less optional. I just liked the project. We heat almost 4000 sqft and our electric bill in the coldest month was about 100 USD. Colleague of mine has a house of the same age but half the size and his NG bill was 350 USD in the same period. My estimation is that we save minimum 600 USD/year on energy.
We live in a barn (aircraft hanger) converted to a house. 0.7 ac leaky pond.
