Hi folks,

Could someone suggest alternatives to an on demand water heater for my off grid house? I know people say they are the only way to go for off grid living, but I've had nothing but trouble with my Rheem.  And the techs who come to try to fix it cost a gazillion dollars. I am fed up with on demand. The error code says it is the heating element, so I replaced that for $300, but it continues to crap out when I am in the middle of a shower (on the third floor, and the unit is in the basement of course), and I have to schlep to the basement, turn it off, then turn it on, and then I get another 5 minutes of water till it does the same thing again. And the error code always says it is the element - which I replaced.  I am tired of throwing money at this thing, and I don't want to get another one.

I asked a local contractor/architect neighbor about putting in a batch system, that is a passive preheat heated tank connected to a regular propane water heater, but he doesn't know what I'm talking about and doesn't want to deal with unfamiliar systems, I think. And no one seems to make such systems, I guess they are always DIY. I even wondered about adding a small inverter and panels etc JUST for a Marathon electric water heater, but...that seems looney, and probably impossible really, though I would love to have a Marathon super insulated heater. I gather there is no way to super insulate a regular gas fired heater because the area being heated is always exposed, and the vent loses heat too. I think those are the central problems.

Any ideas, folks, or am I stuck with on demand because I am off grid?

Mant thanks for any help.

Sounds like you want a propane tank water heater, perhaps with something like this plumbed before it.

What size is the on-demand unit? How are you powering it? How do you provide for pressurized domestic water? What I am getting at is are you sure you don't have a power supply or flow issue causing the heater to fault?

Well, I had wondered about a flow problem, but when I asked Rheem, they said the error message was about the element. Of course, my printer tells me I'm out of paper when there is PLENTy of paper in there, so why not a flow problem and the error message is wrong? Could be.

The house is basement, first floor, second floor, bath on both upper floors. The well sends the water to a reserve tank, and then a pipe that angles down a bit connects the tank water to a basement boost pump. The boost pump (I think I have this right) sends the water to a large 60 gallon pressure tank, which sends it up to all floors. The pressure is fine everywhere UNTIL the pressure tank gets low. At that point the water pressure drops noticeably for a couple of seconds, the boost pump kicks in and the lights flicker for a split second, then as the pressure tank fills the water pressure returns. Usually, (NOT always) the water goes cold after this routine. However, sometimes the hot water craps out even if there is no drop in pressure, no boost pump starting etc etc. So I'm just baffled. And of course none of this happens when a contractor is here looking at the Rheem. I can't fix this if I have I don't know what the problem is - and no one knows.

But I was wondering about my solar as a source of the problem. For example, I had a water softener hooked up, but the cleaning cycle often would not shut off and the softener drained my reserve tank. The softener guy said I could solve that by adding a battery backup between the softener and the electric socket that connected to the softener gadgetry. He said there was (at some point , I forget when this happens or why) a split second delay in my electric current to the softener. My neighbor had the same problem and told me the guy's battery backup fix worked. Could there be a similar problem with the water heater? Some kind of split second interruption in power that results in the Rheem shutting off?

Sorry to be so long winded, but if anyone can help me with this, either with alternatives to on demand or with a fix for the Rheem, I would be most grateful.

> Some kind of split second interruption in power that results in the Rheem shutting off?

Sounds plausible. You have batteries + inverter + a booster pump (and some other devices) with a high starting surge? If so, some possible solutions are bigger batteries, a bigger inverter or a pump with less startup surge (perhaps by modifying the pump circuitry).

Using a UPS by itself (not plugged in) to power the Rheem would be a good test.

True or modified sine wave inverter? Your pump is an inductive load and when that kicks on that could be causing havoc with the heaters power. Trying a UPS on the water heater would be a good troubleshooting test.

"The water pressure drops noticeably for a couple of seconds" That could also be your culprit right there, as it sounds like your water system is not setup correctly.

I have a well. The well pump is our pressure source and feeds thru about 150' of line to a checkvalve and into a large 4 way manifold. There is a pressure tank like yours off of this manifold, the water supply feed into the main house is the leg opposite the inlet. A drain valve is located off the fourth leg with a pressure tap for the pump control switch. The switch is setup to cycle the pump on at 40 PSI and off at around 60 PSI. In operation, I do NOT detect any noticible pressure drop at faucets or while showering.

In your situation, a couple things I would check:
1. Switch cut-in and cut-out pressures. I would set the cut-in pressure no lower than 40 psi. The cut-out can be anywhere above that, as all it really does is determine how much volume gets stored in the pressure tank to control cycle times. IE a small difference in pressures or a small pressuretank means the pump will cycle more frequently. IF it is too low, when the pump kicks on, it not only needs to meet your use demand, it is also trying to recharge that massive pressure storage tank. This sounds to me like your issue.
2. Plumbing between storage tank and pressure pump. Any restrictions here can cause your pump to have difficulty building pressure and rated flow. Basically this line should be very large with nothing in it except a oversized gate or ball valve that can isolate the storage tank from the pump for maintenance/repair. It is far better to push water than to try and pull it. Ideally, the pressure pump would be connected as close as possible to a valve off of the bottom of the tank. Better still would be a submersible pressure pump IN the storage tank with nothing to inerfere with it's water supply...
3. Pump size, power supply and wiring. Pump might not be sized to meet your flow demands. That in conjunction with a low cut-in pressure could cause issues. AC umps are inductive and rely on the AC waveform to operate efficiently. They do not work as efficiently on modified sine waves, which leads to the wiring. To compensate for a poor waveshape, the pump motor will pull more electrical current. Your inverter might not be happy with the surge load(flickering lights) and your wiring might not be sized to meet the pumps current demands under your power source... There is a way thru some creative plumbing to mitigate this electrical startup surge load a little, I can describe it if you wish.

Good Luck.

Any hot water heater (or heating system) that requires power is a lousy choice for off-grid situations. There are many non-condensing tankless units serving up hot water in parts of the world where grid power is unreliable. One US vendor (based in Puerto Rico) is Marey, which makes a number of dumber than a box o' rocks small to mid-sized propane & gas sized on-demand units that need no power:

https://www.marey.com/english/products/gas-water-heaters/duct-exhaust.html

https://www.marey.com/english/products/gas-water-heaters/duct-exhaust/power-gas-16l-ng-dp-ga16ngdp.html

Bosch used to have a number of tankless units that didn't need power too, but I haven't scoped out their off-griddable units recently:

http://www.bosch-climate.us/products-bosch-thermotechnology/gas-tankless-water-heaters/residential-water-heaters/

(Anything that has an LED or other display needs power- look at the ones with with just dumb knobs, no displays.)

These things aren't as efficient as a condensing tankless but they're cheap, and not going to chew power. Having only stupid thermo-mehcanical controls, they're not even capable of spiting a code and stop. They will of course, have some of the quirks of their bigger-deal powered versions (the "cold water sandwich", etc), but the only thing that will shut them down mid-shower would be an over-temp sensor, or a truly major disruption in fuel pressure. I lived with a cheap ~120,000 BTU/hr input tankless like that for over a decade, and retired it still working when did a major make-over on the heating system, integrating domestic hot water into that system. The biggest PITA was having it flame out at low-flow due to over temperature, followed by slow fill times for bathtubs in winter (local climate matters). Better units will have a lower minimum firing rate than mine did (IIRC it was about 30,000BTU/hr, min) which fixes some of the temperature stabilty issues at low flow and the potential for overtemp shut downs.

Of course, an atmospheric-drafted propane water heater with a standing pilot ignition gets you there without power too, but it has a lower overall efficiency than an ~85% (steady-state) efficiency no-power tankless, which has near-zero standby loss in comparison.

An electric tank HW heater is simple and is a cheap way to store the energy, but it's a high-draw load, and backing it up with batteries is prohibitively expensive- truly loony indeed!

Thank you for the reply, but I'm not quite sure I follow. Could an over temp sensor be my problem? I can't see fuel disruption being the issue. Is your guess the temperature sensor?

And are you recommending the heaters in your post that you linked to? It seems likely to me that if I bought another on demand unit similar to the Rheem I have now that I would have the same problem. Boost pump, pressure tank, water softener, inverter etc etc - the problem could be anywhere. I mean, I don't even know WHO to ask to investigate this system. I need someone who knows off grid solar, and plumbing, and on demand heaters, and wells. For example, a city plumber friend of mine came out to my place, stared at the pressure tank and said "What's that?" City electricians look at the inverter/charge controller etc and scratch their heads. How do I find someone who understands how the entire system works all together?

To live off grid, you really need to be self-reliant and fully capable of building/maintaining your off grid infrastructure...and enjoy doing so... We use solar and hydro power for our electric Stiebel Eltron tankless water heater and our NextGen boiler without any issue. You might want to visit:

Build-It-Solar

I've been in my off grid home for 12 years, and somehow, silly old me, I've managed.

I haven't used any of the no-power Marey units, but I have used the older versions of the unpowered Bosch. They're OK as long as you have expectations set appropriately.

The complexity of the controls of the old-school tankless water heaters are an order of magnitude lower than an all-electronic feedback Rheem, with far less sensitivity to things such as fuel & water pressure fluctuations. All thermo-mechanical feedback isn't necessarily easier to debug when it screws up, but there are fewer individual points of failure than the more sophisticated electronic controls. If they can work reasonably reliably on a gravity feed cistern and a small propane tank in back of a shack in Guatemala it should work reasonably well for you.

But an atmospherically drafted propane fired tank hot water heater would be even simpler, and even more trouble free, since they're even less sensitive/more reliable.

Debugging something as complicated as a tankless by web-forum isn't very efficient, but to even start it helps to have more information than what has been provided. What we have so far is the equivalent of "My Ford keeps stalling in in the middle of traffic every time I try to accelerate through a right turn." Is that a 1962 F100 pickup truck, the 1989 Escort or a 2011 Fusion Hybrid? Any one could have that sort of symptom, but the reasons would likely be different. In order to narrow down and zoom in on the possible explanation for your tankless hot water intermittencyissues, it helps to know at least a few things such as the model number and age of your Rheem tankless.

An electric tankless may require more inverter and battery than you have, even a standard electric tank or Marathon isn't necessarily desirable, unless you only enable the heating elements when there is adequate PV power available to not have to (ab)use the batteries very much.

I seeking the best tankless water heater for my family, I think in terms of flow, not capacity. As discussed in this review, a tankless water heater are responsible for heating your home’s supply of water and immediately supplying that hot water appliances. But it may not heat water fast enough to serve multiple fixtures at once. How do you think which water heater to choose? What characteristics should have a water heater?