A customer claims that their heater needed to be replaced because the heat exchanger went bad. The installer claimed that it was due to improper chemistry. I personally handle this pool, and the chemistry has been maintained within the acceptable ranges since I started caring for this pool. I'm willing to accept that the chemistry was not perfect at all times, but it certainly wasn't too far off.
This customer has been a pain in the butt from the beginning, and is just one of those people that makes you feel like you need a shower after talking to them. In the past, there was a problem with his DE filter. The pool builder told him that the grids broke because someone vacuumed with the filter on backwash. This of course is ridiculous. What good would a pool filter be that didn't allow for vacuuming out algae. When this happened, I contacted the manufacturer, and they confirmed that vacuuming on backwash was perfectly acceptable. So I suspect that this is a case of a crappy pool builder trying to blame everything on the company maintaining the pool to get out of having to warranty their installations.
So how quickly will corrosive conditions eat through a heat exchanger? Just how corrosive would the water need to be to do it in only a few years? It seems to me that the pH would have to be pretty low all the time to eat away enough copper to cause a failure in only a few years.