If you haven't changed the anode rod on the 6 year old one, I'd suggest replacing it very soon. Mine was decimated at 4 years. One of the main reasons why hot water heaters fail - after the anode is gone, the next metal that is sacrificed is the heater elements, then the tank itself until it springs a leak. Then you are replacing the entire unit. These hybrid water heaters are expensive, and getting even more so. Replacing what I bought seven years ago would cost me 2.5x what I paid before - and that's just for the unit itself. Replacing a $30 anode rod is a great investment to extend the life of the unit.
Just trying to help!
Here's what mine looked like after four years with Florida water chemistry and sediments. These new are almost three feet long!
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