Bostech Services has serviced my tank-less hot water heater. They've come out a couple times to service it, do work, and do maintenance on it. It's been okay. They're trying to get me to a better place than when I started. I had it installed by someone else and they installed it incorrectly, so Bostech has been trying to get to me to where I don't have any issues.
They've come out four or five times over the past few years. I brought someone else in before this last visit and it was clear that this new person didn't know what he was talking about. So I feel comfortable with Bostech's technicians in terms of their knowledge, thoroughness, and desire to make this situation better. They're pretty good and I would recommend them.