Leaking Navien CR-240 Heat Exchanger - replace or repair?

[Eagle11]

I purchased a CR-240 in 2009 and had several components replaced under warranty in 2011 when it started leaking, but it has been reliable since then. Yesterday it stopped working, and when I checked, it was without power. I checked the internal breaker, which had tripped, and it was wet but no water had escaped the housing. Further investigation showed a small pool of water that had collected, and subsequently overflowed, at the seam between the two heat exchanger components. This water had then dripped down on to the breaker which had tripped.
I called the plumber that installed it and they came out and checked the situation and agreed with me that the primary heat exchanger was leaking after running some pressure tests. He explained that even though the heat exchanger was under warranty and could be replaced that it would be better to go with a new unit because the cost of labor to replace the hear exchanger would make it not worth it. The unit he would replace it with would be a "newer model" but the cost would be $1,800 for the heater and installation.
Does this sound reasonable, or should I be pushing for the warranty replacement of just the heat exchanger?

 

[Dana]

See if you can't get competitive bids on replacing just the heat exchanger. The installed price for replacing the whole thing sounds about right though- it might even be on the cheap side if it includes replacing the venting as well. Navien's seem to have improved in both reliability and design over time.

If the heat exchanger warranty exchange comes in at a grand the full replacement starts looking more attractive. If it's only a couple hundred, swap the heat exchanger.