One caution; and this is true with others:
The on board circ is only good for producing 5gpm through the primary loop. You cannot change it out for a larger one as it is proprietary.
This should not be an issue with radiant as the will be a large Delta T between the primary and secondary. However, if you're connecting it to baseboard system that's looking for 170* average water with a 20* Delta T, you're only gonna get 50k btu's regardless of the boiler's input. None of the manufacturers tell you this and I've pinned the the ears of more than one rep to the wall in training classes over this issue. They ought to disclose this, but they don't. To me that's deceptive.
Other than that, I've had no issues with Navien combi. They work great.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.