Have you considered the possibility that your system design (water loop, ducts, etc.) or poor installation or repairs might be contributing to your unit failures? What type of water loop do you have? Have you read the first sticky thread in this topic titled "Problem with your heat pump? Start here......." and are you able to provide answers to the questions posed?
Here is a direct link to the thread:
http://www.greenbuildingtalk.com/Fo...fault.aspx