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What would make my Eccotemp 40HI-NG tankless hot water

heater incapable of maintaining the...
What would make my Eccotemp 40HI-NG tankless hot water heater incapable of maintaining the temperature that is set at? The unit had been dripping a bit. However, after two hours with the submersible pump circulating vinegar through the system followed by two hours of Whitlam Flow-Aide being circulated, there appears to be no dripping now. Before the flush, the unit had stopped heating. Now the water overheats by as much as 13 degrees and underheats by as much as 60 degrees. Is this the fault of the electronic board that the temperature cannot be held constant and the board is in need of replacement. If not the board, what part is at fault?
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Customer reply replied 4 months ago
The flow sensor seems to be working as the gas burner turns on and the fan may kick in as the tankless tries to heat the water. There is no telling what it will do temperature wise and how long it will run at one temperature before raising or falling to another temperature or just giving only cold water. During all of this, no error code shows in the window--only the rising or falling temperature displays there.
Answered in 3 hours by:
2/18/2018
Mike R.
Mike R., Plumber
Category: Plumbing
Satisfied Customers: 3,042
Experience: 20 years of plumbing experience, including high end homes and service work.
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Hi, I'm Mike and I have 20+ years of experience as a plumber. I'll be glad to assist you today.

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How old is the water heater and has it ever been serviced?

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Customer reply replied 4 months ago
Professionally installed Feb 2011. Maintained by flushing one a year. There is only one person in the house so there is not much water that is heated.

How recent was the last flushing?

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When the temperature fluctuates does the flow do the same? Any idea where the water was dripping from? Was it dripping from inside the casing or from the temperature relief valve?

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Customer reply replied 4 months ago
No the flow is consistent while the temperature fluctuates. It was dripping from the inside the cabinet.

So far I would say that there are several issues. There is an ignition control board and a main control board. The ignition control board is likely the only board I would replace. The issues are likely caused by previous blockages in the heat exchanger that were not totally cleared from the flushing. The blockages have caused a crack somewhere in the heat exchanger and the high limit sensor does not seem to be working also. I would for sure say that the heat exchanger and high limit sensor certainly need replacement. The main board seems fine as the temperature is displayed correctly and the high limit sensor is not relaying to the board for an error to be displayed.

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Honestly I am not sure how much a heat exchanger is for that unit but based on the age and what my guestimated price for a heat exchanger would be I would guess you will only be saving about $200 by repairing it yourself vs. replacing it with a like unit yourself.

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Customer reply replied 4 months ago
These are the replaceable parts within the tankless. https://www.eccotemp.com/40hi-h-parts/ A heat exchanger cannot be purchased for the unit. Can it be further flushed to make it function properly? . So looking at the parts at the site, can you please tell me which of them as found in this tankless are the ones with exception of the heat exchanger you think need to be replaced? This unit has 3 inch venting so replacement of the venting alone it going to be about $300 before a new unit is even thrown into the total cost. If I have to get a new unit, so be it. However, I will try parts replacement first if possible.
Customer reply replied 4 months ago
Why after the cleaning has the dripping stopped?

Honestly there is a very good chance that a heat exchanger will not be available. Considering the issues and the fact that it was leaking internally would indicate that the heat exchanger being replaced is the only way to get it running again. Is there a single vent or two? As far as the exact parts none of us just look it up online. We usually confirm part numbers by removing the part from the unit or in this case would get the correct part number directly from the manufacturer. The cleaning has likely moved the blockage inside the heat exchanger into the crack and blocked the leak. That leak will start again and it will get very large as you use the unit. It is also very likely that the venting on the unit can be re-used so almost certainly a new unit will be the only thing you need for a new one. It should be a pretty easy replacement as those units are only about $400 and I am guessing that a heat exchanger is going to be about $250-300 if you can find one at all.

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Is the vent one pipe or two? Does the pipe go directly out of the wall?

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Customer reply replied 4 months ago
It is one vent and three inches in diameter stainless steel. Nothing that would be a replacement for this heater now uses venting that small. A Rinnai would use 5x3 venting and even another Eccotemp which I would not buy would uses 4 inch stainless steel. It would be complete venting replacement.
https://www.eccotemp.com/40hi-ng-over-temperature-sensor/ Is this what you are speaking of? I just want to get through about a month until I have time to get a repair person in to put in a new Rinnai unit.
Customer reply replied 4 months ago
Or I can take this unit off the wall and send it to Eccotemp for repair. Do you think they can repair it?

I really doubt that repair is going to be feasible. If you sent it to be repaired I am guessing that would be more than the cost of a new one. The venting should not be metal anyway. I am guessing that this water heater replaced a tank water heater and they used the old vent? Is the water heater nearby an outside wall now? Rinnai is kind of expensive. For less than the cost of a 7.5 gpm Rinnai you can get an 8.4 gpm Rheem and it comes with a piece to put outside for the vent cover then you just run PVC pipe to vent outside.

Mike R.
Mike R., Plumber
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Experience: 20 years of plumbing experience, including high end homes and service work.
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Customer reply replied 4 months ago
Thanks for the Rheem suggestion. The PVC would be a lot less expensive than the 5x3 required for the Rinnai. I will take a look at the Rheem. I presume Rheem has a 8.4 gpm a one vent tankless; I don't have room for two vents. And no, the Eccotemp 40HI-NG required the 3 inch stainless steel venting. The previous standing hot water heater vented up and out with the furnace. It did not have to vent out like the tankless. So do you think the hi limit sensor will help me make it 30 days or should I just try to limp along without it? Thanks for everything. I am going to rate you with 5 stars now and I hope you can answer my last question about the hi limit sensor.

Replacing the high limit sensor will cause it to get the error code. It will be safer to use with a working sensor but it likely will not work at all. I am sorry to say that it is possible the water heater will not work again. Also the Rheem vent is two separate pipes but they can go pretty far. They just go straight out of the wall. The limit may be 20 feet or so. One is intake and one is exhaust. The shorter the vent on a tankless the better.

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Customer reply replied 3 months ago
Can't do the intake and output combo. There is not enough space for that. You can't vent into the furnace flue with a tankless so it is the 3x5 more expensive venting for me whether it is Rheem or Rinnai.I will need 15 feet of total venting, an elbow, and the outside hood.
I had had the water heater at 125 degrees. I dropped it to 118 degrees and that seems to work for now. Meanwhile I am looking at the Rheem and Rinnai warranties. When you have to vent out with 3x5, the prices for the Rheem and Rinnai are about the same, but it appears the Rinnai warranty is much better. Last but not least, if the heat exchanger goes bad in the Rinnai, it is a part that unlike the Eccotemp can be replaced. So I've still got to see if Rheem like Rinnai has heat exchanger replacement parts and pays for labor when parts under warranty have to be replaced. Then I can make my decision. Thanks again!

You are very welcome. Feel free to request me for your next question. I will always go the extra mile!

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Customer reply replied 3 months ago
I will add you to my favorites!!

Most excellent!

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