I've read many negative comments of early Navien products. Apparently the original products fall into two areas; either faulty parts or poor installation and unfamiliarity by plumbers and diyers with troubleshooting.
My understanding is tankless water heaters are standard in Europe and Asia so this may make tankless products a new learning curve in America. Fortunately my choice seems to be an exception to negative reviews as my installation occurred two months ago and now using heat for its first winter. A licensed plumber trained in Naviens transformed a standard hot water boiler for a 3-zone hydronic system and dhw heater into one tankless unit with all new plumbing already cutting my monthly gas bill in NYC. Heating is perfect and silent.
Hot water is perfect although there is a delay but acceptable once old habits change (instead of turning on full hot water to the tub then switching to shower, the shower is used to reduce water flow while allowing heating to occur in less than a minute). My old boiler ran out of hot water all the time when filling the washer but now fills with hot water. My guess is original Naviens were problematic with early teething pains, discontinued and then reintroduced to the market with upgrades. If I'm not mistaken, mine is the top of the line product and seems to be trouble free, meeting its specifications.
Having a licensed plumber familiar with Naviens to make a brand new installation incorporating all the external plumbing parts for correct installation may be another key to a successful changeover from tank to tankless. My cost is not inexpensive but a quick calculation of savings on gas usage shows a break even point as early as 8-yrs provided nothing breaks.
Reason of review: Good quality.
I liked: Professional installation with attention to detail.