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Is there a Marathon-esque tankless water heater with a lifetime warranty?

bluesolar | Posted in Green Products and Materials on

Ahoy — The Rheem Marathon water heater has a lifetime warranty because it uses a polybutene tank as opposed to steel tanks that are destined to corrode and fail.

Question: Are there any tankless water heaters with lifetime warranties? Anything built to an equivalent standard of longevity as the Marathon?

Per, conventional water heaters with tanks last about 12 years, while tankless models last about 20 years. Let’s conservatively say that the Marathon is good for 40 years – I’m interested in knowing about any tankless models with that kind of lifespan.

I’ve attached a diagram of a tankless water heater – what is going to fail here? It’s the tanks that fail in conventional models, so what components in tankless models are limiting their lifespans to ≈ 20 years?

Thanks for your help…


Rheem Marathon:

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi BlueSolar.

    My understanding is that one of the biggest problems with tankless units is neglected maintenance. Well, I guess the problem is actually hard water and scaling inside the unit. But this can be taken care of with regular flushing. I believe that a high enough water flow rate (GPM) is also important (not only for longevity, but for efficient operation). And some people address the hard water issue before the water enters the water heater with a water softener.

    Looking forward to others responses to this post because I don't know much about tankless water heaters...

    1. bluesolar | | #4

      Oh, that's right. I remember reading something here about well water being hard on tankless units, and how people were using whole house water filters before hitting the tankless heater.

  2. Expert Member
    Akos | | #2

    As Brian pointed out, the main issue is scale buildup. Anything that needs regular maintenance gets neglected over time.

    If you open up one of the modern units, there is a lot of wiring, sensors and components in there. Despite that complexity most are extremely reliable. I think it would be impossible to make one as reliable as a tank water heater, there is just way more "stuff" in there.

    Depending on what you use them for the wear item will be different. For combo heat (much longer run times), sometimes the blowers or the electronics can fail. The units have an igniter/flame sensor both could fail over time especially if the unit is cycling a lot.

    The units have a flow sensor and an electronic mixing valve, both of those could fail with scale buildup from lack of maintenance.

    Any fuel burner has corrosive exhaust, this will corrode the heat exchanger over time. They are extremely well designed, but will eventually corrode, no such think as lifetime warranty on those.

    1. bluesolar | | #3

      Thanks Akos, this is great info.

      Question: Tank water heaters apparently have some sort of recovery time after the tank is depleted, during which time there is no hot water. Why can't they do what tankless water heaters do and heat water on the fly when the tank runs out?

      I thought that this is what hybrid water heaters do, but it turns out that hybrid means heat pump...

      1. GBA Editor
        Brian Pontolilo | | #6

        Hybrid doesn't mean heat pump. "Hybrids" are a combination heat pump and electric coil. The heat pump is super efficient, and the water heater can be set to use only the heat pump. The electric coil can be used (again, depending on the mode you choose) to boost the recovery rate.

        I'm not aware of any tank style water heaters with an instantaneous heating feature as you describe, but I have seen builders put a tankless unit in line in front of a storage tank unit, similar to having the supply pre-heated by the heating system's boiler.

  3. George_7224612 | | #5

    Tank water heaters do heat on the fly, but the electric heating elements or gas burner don't have the same heat output as a tankless. As hot water leaves the tank and is replaced with cold water, a thermostat turns on the heating elements, so they're hard at work trying to get the tank back up to set point. The more hot water you run out of the tank, the longer it takes for recovery. If your water heater is appropriately sized for normal use, you'll probably not run out enough hot water for it to be a problem.

    Hybrid water heaters (HPWH) work differently in that they have a heat pump in addition to electric heating elements. They can be set for different combinations; heat pump only, heat pump and electric elements or electric elements only. Small households can often get away with using only the heat pump and save a substantial amount of electricity. There are only two in our household and we've never used the electric elements.

    1. GBA Editor
      Brian Pontolilo | | #7

      That was my experience as well, George. And we had three in the house a lot of the time.

  4. bfw577 | | #8

    Tanks will last a long time if you replace the anode rod. Pretty much nobody does. I have replaced 2 so far on my geospring HPHW. My uncle still has an electric tank from the mid 80s. He changes his anode rod every few years.

    Here is what my anode rod looked like on me geospring after a few years. A new one runs almost all the way to the bottom of the tank.

    1. bluesolar | | #9

      Does HPHW stand for Heat Pump something or other? Heat pumps have anode rods?

      1. bfw577 | | #12

        Yes. Heat pump hot water heater. Mine is one of the early verisons the GE Geospring. Been running 6 years nonstop in heat pump only mode. I got lucky as there was a $1000 rebate so I paid a little over $100 for it. The rebate is still available for $750 and most New England states have really good incentives for them.

  5. exeric | | #10

    I think the more interesting and relevant question is not the original question posted but a slight variation on it. It would be this: Is there a HPWH that has a corrosion resistant tank like the Marathon resistance heating water heater?

    The answer is "no" as far as I know. If there was such a thing and the price was not exorbitant (big if) I think people would beat a path to the manufacturer's door. I have a Marathon and bought it because of the longevity. It gets pretty old experiencing cold showers at the most inopportune times. Actually, it is always an inopportune time. It WILL happen to you with a metal tank. I would really like the low energy consumption of a HPWH but I really don't like the idea that they have as limited a lifetime as standard water heaters. Combined with the much greater replacement expense it turned out to be a no-go for me. It was a judgement call for me that people can reasonably differ on.

    1. bfw577 | | #11

      Most tanks will last the warranty period of 10 years without anode replacement and then rust out. When I first flushed it and changed the first rod the water came out really rusty at the bottom The 2nd time 3 years later there was no rust.

      I would guess 90 percent of people dont change them. With regular inspections and replacement a steel tank can last for a really long time.

      1. exeric | | #13

        I concur with what you said except for one thing. I suspect at least 98% of people don't change the anode. I'm just guessing, of course. I think you are super conscientious and to be commended.

        1. Expert Member
          BILL WICHERS | | #14

          My guess is that most people don’t even know there are any serviceable items on a water heater. The water heater lasts what it lasts and they replace the entire unit.

          Note that there are powered anodes that plug in and don’t need periodic replacement. They cost more though.


          1. irene3 | | #15

            A powered anode is like $120. Not that bad considering how much longer they last, and saving the trouble of replacing them. I'm told it's not a bad job to do (we've never done it due to having very soft water and not being very handy), but anyone would rather do a job once than a bunch of times.

      2. Expert Member
        Akos | | #16

        I'll 2nd replacing the anodes. Have a 25 year old water electric tank on its 3rd anode. Replacing it the first time was a big pain, 4 foot breaker bar+torch. 2nd time was much easier.

        One thing that would really help is taking the anode out on a new tank, putting some teflon tape on it and threading it back in. This makes it much easier to remove in the future.

        1. bluesolar | | #17

          So that Teflon tape stuff works? They ought to ship water heaters with that already in place...

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