I had purchased my Aquastar (not Bosch) about that same time. It is a 125?? model, it is one that measured out going water temp and adjusted gas flow accordingly. That feature only lasted less than ten years, after it quit, I bypassed the sensor and the performance really wasn't any different. A few years after I got it we had a cold winter and the air backflowed freezing and cracking the heat exchanger. After replacing the heat exchanger was just cleaning the pilot orifice and a couple minor things like that.
Overall 25+ years with 5 in the family(2 bathrooms), we always had enough water. The freezing heat exchanger was my fault for not installing the flue properly. But now its time to replace it, I'm shopping for a new one now. Right now it has a pinhole leak in the heat exchanger, drip....drip, and two days ago a crack developed in the control unit putting it out of service for good. Absolutely no idea how the crack got there, but gas leaks through it when it starts, not good, it wasn't there a couple weeks ago when I was looking at it.
Well these things aren't meant to last forever.