If you own, install, or service Navien equipment...

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Navien tankless water heaters, boilers, and combi-boiler with water tube heat exchangers have a generally good reputation. Now the bad news...

There appears to be high failure rates of the exhaust vent gasket at the sheet metal under the vent collar, and failures the combustion chamber seal at the heat exchanger. I'm not normally an alarmist, but this is both a safety and reliability concern. If you've ever opened up the unit to see oily film on things, it's either this type of failure, or cross contamination of the intake air and exhaust due to improper installation/location of the intake & exhaust vents being too close to one another.

The gasket and combustion chamber seal failures are likely restricted to Navien's water tube heat exchangers, but that would include most models. Their fire tube heat exchangers are very different, and unlikely to fail in the same way.

This guy on Long Island up until a few weeks ago was a big proponent of Navien equipment, but after replacing dozens of heat exchangers, and recently replacing the heat exchanger on his own NPE 240 discovered that the brand new heat exchanger right out of the box was leaking at the combustion chamber seal, and has now flipped 180 degrees.

The shorter video explaining where the problems are and how they can be diagnosed lives here:

A longer video showing a brand new warranty replacement heat exchanger that failed right out of the box lives here:

<It's a bit tedious- scroll forward to the 49 minute mark as he's filling & purging the unit after replacing it, followed by the initial firing and testing for leaks with soapy water.

These are some of the most popular tankless gas water heaters and combi heaters in my area. YMMV.
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