A different possitive for tankless?

Installers...I need you tell me if thought is true or false or unknown.

Once I install a tankless unit, do I never NEED to 'unplumb it"?

I ask this in the form of a question because I dont know the answer, but in my head it would appear to be true because these tankless units are much like furnaces now.

Hot water tanks have to be replaced every 10 years or so and that requires moving the old out and bringing in the new and replumbing the gas and water is always required.

On tankless, all the internals are replacable, like a furnace. Right?

If so, technically speaking, is there ever a reason I would have to replace the whole unit?

It should last a long time IF you maintain it. It will require more maintenance than a stand-alone WH tank. If you don't make provisions to delime it periodically, the performance will drop and it could stop working in a worst case because the flow through it is so restricted that it overheats internally since not much water is passing through. It's nice to be able to replace it easily, when the time comes, since like anything, parts won't be available forever, too. At some point, it WILL need to be replaced, but it could be awhile. Pick the 'wrong' brand, and parts could become nonexistant next year...then what do you do?

Even with the RIGHT brand, assuming parts-availability 15 years out would be a dubious bet. Unlike the automotive industry, there is no regulatory requirement on the manufacturer to maintain a stock of repair parts. At the limits of the warranty period it could be tough going.

OTOH, lugging in a full-replacement tankless is a relatively easy 1-person job, compared to a tank. ;-)

[edited to add] Note, the standard warranty on most tankless heaters are longer for the heat exchanger than for the rest of it.

Navien gives you 15 years on the HX, 3 on the rest.

Takagi give you 10 on the HX, 5 on the rest

Rinnai offers 12 on the HX, 5 on the rest for some models, worse on the others.

Noritz is a 12 & 5 type of company too.

So, 5 years out, if you need a non-heat exchanger replacement part it may be available, but don't count on it much after that.