I currently have a Bard Geothermal unit. It was installed when we built our house 6 years ago. I have 2 questions. 1.) I have used a Taco Zone Valve. The first was replaced March 2011, and I just had this one replaced a couple of weeks ago. They had problems not closing and water was continually flowing through them, even after they were checked for debris. This time the installer used a regular irrigation valve, which seems to work, but it does have a hammer. Could this harm my unit? 2.) I had a warning a couple of months ago. The installer says my coil has a leak and should be replaced. I was also recommended using some sort of sealer that was sprayed from a can. Are there any opinions about that?

Taco valves are the best mid-ranged priced valves, but will fail.
There are more expensive models and cheaper as you learned.
Slow close valves are preferred and while you likely won't damage the geo, water hammer is force that will attack something.
Not heard of a spray on leak repair.
good luck,
joe

Most refrigeration guys will cringe at the thought of anything other than refrigerant in a heat pump. It may allow the contractor to get paid but someone will be back to do way more work after. If you want a good professional valve look up Belimo valves. You can get a SS 2 or 3 way ball valve that will do what you want. Yes, It will cost a bit more but you will only do it once.