Be aware that high efficiency units have blower/fans and can be a bit noisy if installed where noise is a problem, Through the years most circ pumps were not on timers and ran 24/7 1/2 inch copper circ lines really had trouble with pinholes and leaks in the fittings due to the copper pipe not being reamed when installed, We now install pumps with timers as it is code,many times I ran across pumps with to much head pressure or volume that really gave the recirc line a workout, I know the area rep for Eternal and he could give you a pep talk about his unit, Navien is just a few miles away so I see the reps at the local plumbing supply's frequently doing little sales pitch seminars etc.
Fluffy, you make a very good point and one I always pass on to customers who really want a tankless, I will do a backflush and a quick once over if there is a problem with a unit I installed, if it is internal I call the area service rep for that brand, as here in So. Cal. they are abundant,
