One of our customers put in one of these with a recirc pump, so it runs constantly.
Betcha it doesn't last very long. I believe they have a duty cycle or at least are designed for intermittent duty. Also, a recirc pump pretty much goes against what the heater was designed for, that being on-demand water heating. If it's going to maintain hot water there are other much less expensive alternatives such as a conventional water heater.
-Hal
