Navien Maintenance NR-240A Tankless Water Heater
Maintenance Navien Water Heater
To Date, I have done very little maintenance. I have taken off the intake vent cover once (as of Dec 2012), and sent the vacuum hose down to remove bug and dust debris. That is it.
I do have a water softener to ensure the water is soft going in to the water heater - important as hard water is a fact of life where I live.
My feeling is that to compare water heaters, you need to compare maintenance levels too. Most manufacturers recommend you flush your tank heater every few years, but most people don't bother to do that now, do they?