The heat in the basement unit of my two-apartment home kept overheating: ET sent a tech very quickly, and returned a verdict of a stuck zone valve. After ordering the part, they came back a second time free of charge to determine why I was having to replace it so soon: I had just had another zone valve repair a few months before.
Together, we determined that it had been a different valve than the one which needed replacing now. Disappointing for my wallet, but they were professional and weren't upset at all with my forgetfulness!
The plumber who eventually replaced the part was excellent, and made sure to test things for me as well as explain what was happening. I am completely satisfied with their work!