what is this rustic water come from--New tankless water heater

[yan2hua]

I just intalled the GE tankless water heater. The hot water line will have about 10 seconds rust like water if it it not used for a day. So every day morning, there is about 10 seconds rust like water. The rust color will be more dark if not use hot water for a longer time. The plumber checked and checked again and said it is the tankless water heater unit problem. Called the GE tankless water technician support, they said there is no any possibility the "unit" can produce the rust because it is make by copper in the heat exchanger. So no one can find what this rust color water come from. See the attached illustration drawing for details. Hope I can get the answer here.

[Gary Swart]

I'm not a fan of tankless water heaters, but putting that aside, rust can only come from iron or steel. Are you absolutely certain there isn't a steel nipple, coupler, or union in the hot side portion of the plumbing? Not to foist the blame on the plumber, but I would accept the manufactures statement that they do not make their units with steel components. If they did, this would be a huge problem for them because all of their heater would show rust. I would not go so far as to call the plumber a liar, I'm sure if he used a steel component it was accidental, but there has to be some steel in there somewhere.

[Dana]

It's probably not iron oxide-it would require and extremely high oxidation rate to discolor it overnight in such a short segment. It could be something biological. (If you're brave you could taste it and probably determine if it's iron. :-) )

[Gary Swart]

I yield to Dana. He has far more knowledge of tankless heater than I. Perhaps a chemical analysis would be in order...just a little more scientific than the taste test although I doubt there would be any harm in tasting.

[Brahms]

I don't see where you say what your water source is. I have two Rinnai units, one at our "town" house fed from chlorinated city water and one at our cabin fed from our private well in the fractured marble/granite typical of the Piedmont in North Georgia. The "town" house unit never has any rusty discharge. The cabin unit frequently has what looks like a rusty discharge. We have very high iron content in our well in seasons when we don't get a lot of recharge from rainwater, or when we don't flush the well completely. At the cabin we also frequently have iron stains in our toilet, same reason.

If you have a private well, or if your public water source is a well (as opposed to a river or lake), I suggest you get a water sample to your local health department or a commercial lab and ask them to check it for iron content.

The technician is likely correct. When the heater heats the water, the iron falls out of solution. Very simple chemistry. High iron can be corrected by installing a green sand filter. Or you can put up with it and consider it an undocumented feature of the system. Beats having to take multivitamins.

For what it's worth.

[yan2hua]

Thanks for your comments and suggestions. Here are more information and testings: 1. the water source is city water and it is drinkable. I have another tank water heater with no any problems. 2. The first picture is the total amout of the rusty water will come from the hot water outlet right after the tankless heater. after this amount, the water will be clean. 3. the second picture shows that rusty color stuff will start to deposit to bottom after a day. 4. the close look of that rusty stuff, what is it ?
Thanks.

[Dana]

You may be getting the same deposits in your tank-type water heater, but since the hot water leaves out the top and the brown crud sinks to the bottom, it all just collects as sludge at the bottom. Drain a few gallons out of the bottom of your tank heater and see if it has a similar appearance.

It's fairly common for "hard" water to precipitate inorganic-salt solids out of the water when heated. If your city water department probably measures water hardness and maintain records. If water hardness is in the moderately hard to hard range, it becomes something of a maintenance issue for tankless water heaters, since some of those solids end up sticking to the heat exchanger, and need to be rinsed out every year or so with mild-acid flush to keep it flowing well and running efficiently. (Read up on what to use and how to do it before doing it yourself.)

[yan2hua]

Hi, Here are more testing results, Please help to reasoning the root cause:

1. The deposit can be desovled back to water completely if the bucket is vibrated in couple of seconds. And it will deposit again into the bottom after a day.
2. Had the tankless water heater run in highest temperature (140 F) for an hour. And the rusty color water will be the same as before (at the begining about 10 seconds) when it is not used for a day. The hot water testing outlet is right after the hearter (also, checked and run the cold water right before the heater to make sure it is clear).
3. Turned off the tankless water heater, the hot water outlet will produce about same amount of rusty color water.
4. Checked another tank water heater (it is new), it has no rusty color stuff when drain from the bottom.

[Dana]

If it dissolves when agitated it's definitely not rust.

This calls for a chemical analysis- it's probably a mineral salt of some sort, but exactly what it is (and how to keep it from precipitating) are unlikely to be discovered by a web-forum analysis.

The city water department may be willing to help figure it out- if it's a problem for YOU, it is going to be a problem for many, and if under or over-treatment of the water on their end is part of the problem, they may be able to adjust their chemistry to prevent it.

[yan2hua]

how to explain the test item 3: cold water in (clear) but rusty color(cold too, the heater shutted off) out of the heater, if it is water source problem ?

[Dana]

Are you saying that with the heater shut off you can run it until the water comes out clear, but if you wait over night it then comes out rust-colored?

[yan2hua]

Please see the picture in the begining post. There are two water outlet, one is right before the heater(at the cold water line) and the another is right after the heater (at the hot water line). The water always clean before the heater. The water after the heater will become rust-color if it is not used for a while (may be 12 hours, the more time the more rust-color stuff) even the heater is shutted off ( temperature of the water comes out from heater is not heated, in order to test if the heating will create some changes).

[yan2hua]

The rusty color water will only last about 10 seconds, then clean. it will come back if not used for a while. I have flushed (run the heater in 140 F degree) for an hour, but the rust-color water showed up again right after not using it for a day.

[ballvalve]

put a 1 micron filter on the house entrance.

[wassermeister]

put a 1 micron filter on the house entrance.

You can use a Rusco Sediment Filter in place. You can visually see when there is sediment build up. When it gets dirty you can drain it out. It has a valve that you can open easily from time to time. It gets installed on the cold water line. Red Robin Restaurants have this equipment installed all over the US.