Descaling Navien NPE-240A with no shutoff for Recirculation line

[CMaustin]

New user posting. I am look for guidance with regards to annual descaling of our Navien NPE-240A water heater. I have purchased a descaling kit which includes an external pump, hoses, bucket, etc.

The instructions in the User's Manual (Page 11, 4.3 Flushing the Heat Exchanger) show a configuration that does not have a recirculation connection. My setup is a bit different (see attached image) where there are shutoff values for the hot & cold lines going into and out of the WH but no shut-off (ball value) on the recirculation line.

Opening the cover of the WH I see that the 2-way valve inside the unit is set to EXT.

I contacted Navien and explained that my setup does not have a shutoff on the recirculation line. They suggested that I switch the 2-way value to INT and set the DIP switch 1 to ON & switch 2 to OFF, PRIOR to beginning the descaling process and then switch the 2-way value back to EXT and the DIP switch 1 to OFF & switch 2 to ON AFTER completing descaling.

I want to confirm my understanding of how to descale my unit given my setup? I also want to confirm that the WH should be powered off during descaling (i.e. gas valve shut-off and WH shutoff) as noted in the instruction in the User's Manual?

Thanks in advance for your help!

 

[GReynolds929]

That's how I would do it if there's no shut off on the return line. Don't bother with the dip switches if you have your own pump. Power off at the front panel which will open the inlet solenoid and then unplug from the wall.

 

[Sponsor]

 

[Breplum]

I concur with GR.

 

[CMaustin]

Thank you GReynolds929 & Breplum for your suggestions! I got a chance to try out your suggestions today but didn't have much luck. Here's what I did.

1) From the front panel, powered off the WH.
2) Switched the valve inside the unit to INT.
3) Unplugged the water heater from the wall outlet.
4) The recirculation occurs under the kitchen sink so shut off the recirculation device and also shut-off the hot & cold water values under the sink.
5) Closed the hot & cold water line shutoff values below the WH.
6) Connected the hoses to the hot & cold water by-pass connectors.
7) Opened the by-pass values to drain water from the WH.
8) Connected the hose going to the cold water bypass to the top of the external pump.
9) Put the hose from the hot water bypass in the bucket with the cleaning solution.
10) Plugged the external pump to start circulating the cleaning solution.
11) Once the external pump was plugged in, the cleaning solution started flowing through the cold water bypass hose and as expected started coming out of the hot water bypass hose.
12) PROBLEM: Initially there was a strong flow of water coming out of the hot water bypass hose into the bucket but about 5-10 seconds later the flow rate started to slow down to the point that it was just a trickle. I unplugged the pump and retried it a couple of times and each time the flow rate would start strong but then drop to a tickle after a few seconds.

Any idea what I am doing wrong and why the output flow rate is dropping?

 

[Breplum]

I have done dozens of de-scaling ops with your type set up. No idea what's going on with yours. Sorry. Call the Nav. tech desk.
They won't help homeowners much, but with descale, they ought to be willing to help.

 

[John Gayewski]

Sounds like your pump is junk.

 

[Breplum]

I bring two pumps and long extension cords to every descale. Pumps fail, seize temporarily, trip GFI's sometimes.

 

[CMaustin]

Thank you GReynolds929 for sharing your perspective & experience!

Posting an update on where things ended up to help others who may have a similar issue in the future.....

I ended up calling the plumber who had originally installed our water heater to show me how to descale my unit. He tried doing the same thing that I was trying to do (i.e. flip the valve inside the WH to INT) and observed the same problem. His conclusion was that the valve inside my WH is not working so even when it's set to INT the descaling pump continues to push majority of the cleaning fluid to the recirculation line thus explaining the low flow out of the hot water line after the tank inside the WH empties.

The plumber ended up shutting off the water supply to the house, temporarily disconnecting and capping the recirculation line at the WH and then proceeded with the descaling process.

He came back and installed a shutoff valve on the recirculation line which, moving forward, will allow me to descale the unit without needing to shutoff the water to the house.

I am not sure how common it is for the valve inside the WH to not work but per Navien support an external shutoff should have been install iin the first place vs. relying on the internal value.

Thank you again to everyone for your insights & guidance!!

 

[Nay Lin]

I’m comparing two quotes for installing NPE-240A2. The first quote includes Easy Plumb V2 3 valve set. NAvien web site description is : Navien Plumb Easy Valves (V2) are designed to provide ease of installation and operation as well as for quick maintenance. The 2nd quote does not mention if this option is included or not.

Is it accessory option worth spending extra to add to 240A2 installation? Would it make maintenance easy enough so it will learn to do the annual maintenance of the system my self ( annual service is quote as about $ 250 )?

 

[John Gayewski]

Yes you need the valve set for maintenance.

 

[DFBrandy]

I too have Navien NPE-240A tankless water heater. I am trying to perform the annual descaling of the unit. I attempted this feature earlier this week but ran into a problem. I followed all the procedures in the operation manual and when I tried to pump the distilled vinegar through the system nothing happened. I could not pump the vinegar. I do have a re-circulation line with a cut-off value. The value was in the "On" position. The 2-way pump setting is set at "EXT" and the first two DIP switches are set to the "On" position. What I am doing wrong? There is no directions in the operation manual in dealing with a recirculation line. I did contact Navien Support and they pretty much told to get lost, to much liability to help a homeowner is what they told me.

 

[GReynolds929]

I too have Navien NPE-240A tankless water heater. I am trying to perform the annual descaling of the unit. I attempted this feature earlier this week but ran into a problem. I followed all the procedures in the operation manual and when I tried to pump the distilled vinegar through the system nothing happened. I could not pump the vinegar. I do have a re-circulation line with a cut-off value. The value was in the "On" position. The 2-way pump setting is set at "EXT" and the first two DIP switches are set to the "On" position. What I am doing wrong? There is no directions in the operation manual in dealing with a recirculation line. I did contact Navien Support and they pretty much told to get lost, to much liability to help a homeowner is what they told me.

Post a picture of what you are trying to do. Particularly the connections under the heater.

 

[Bannerman]

What I am doing wrong?

You didn't mention anything about a separate pump to circulate the vinegar solution in a loop, from a bucket, through the heat exchanger and back to the bucket.

 

[DFBrandy]

You didn't mention anything about a separate pump to circulate the vinegar solution in a loop, from a bucket, through the heat exchanger and back to the bucket.

Yes, I apologize. I had a separate pump in a bucket filled with 2 gallon of distilled vinegar. When I started the pump, I held the hose from the hot water side in the bucket and the vinegar never started flowing. I'm thinking that it was to due to the recirculation line valve being in the open position and not closed?

 

[Bannerman]

I held the hose from the hot water side in the bucket and the vinegar never started flowing.

Did you prime the pump & hoses?

Pumps are not great at moving air, so the pump and hoses usually need to be manually filled with fluid before the pump is activated.

The diagram below shows the recirculation flow path for the NPE-240A.

Flow path with the 2-way valve set to internal circulation:

 

[DFBrandy]

Did you prime the pump & hoses?

Pumps are not great at moving air, so the pump and hoses usually need to be manually filled with fluid before the pump is activated.

The diagram below shows the recirculation flow path for the NPE-240A.

Flow path with the 2-way valve set to internal circulation:

No, I did not prime the pump or hoses. I do that and let you know how it goes. Thank you very much for your help.

 

[Mulligan7]

My house, which was built in 2023, has a Navien NPE-180A2 natural gas tankless water heater. It is configured for external recirculation, using the built-in pump. The 2-way switch is in the EXT position. The recirculation line does not have a shutoff valve. In addition to the shutoff valves at the WH, there is an additional inline shutoff valve in the cold-water supply line a foot or two before it connects to the water heater.

It's time to descale the WH. I've done a lot of research on descaling, and I feel like I have an adequate understanding of the process. I bought a submersible pump, hoses, and a few gallons of distilled white vinegar.

Leading up to the actual flushing part of the process, I drained the WH through the hot and cold-water service ports. To facilitate draining, I opened the pressure relief valve briefly a number of times during the process.

I expected the draining process to complete in short order, a few minutes at most. However, water kept slowly trickling out through the cold-water service port. I waited and waited, but the trickling never stopped. After an hour or so, I lost confidence it would ever stop, so I decided to abandon my plans, for now, to descale the WH. Somewhere in the range of two to four gallons of water had trickled out.

Besides just being puzzled where the water could be coming from, I am concerned that if I attempt to flush the WH, the added water will dilute the vinegar, diminishing its descaling effect.

It seems extremely improbable that water could be entering via the cold-water supply line. I turned off both the cold-water valve at the heater and the inline valve in the supply line, and made sure both valves were fully closed.

The only other source of water I can conceive of is the recirculation side of the hot water plumbing, but that also seems a bit far-fetched. With the rest of the plumbing system being closed (fixtures closed, hot supply line closed, pressure relief valve closed) it surprises me that water could be siphoned out of the recirculation pipes. After restoring everything to the normal operating configuration, when I turned on my faucets, there was very little air in the hot-side plumbing.

A couple days later, I made a second attempt. I decided I would do a "rehearsal" flush using pure water instead of vinegar. I wanted to verify that fluid would circulate through the WH via the bucket/pump/hoses rig, and I wanted to more accurately monitor how much water in excess of what I started with might accumulate in the bucket during the flush.

I ran the rehearsal flush for about a half hour. Water passed through the WH as expected, but as time passed, the water level in the bucket continued to rise. At the completion of the operation, I measured the excess water to be a bit more than two gallons.

Assuming that's in the ballpark of how much new water appears in the flushing fluid in a half hour, it's apparent that if I attempt an hour-long flush beginning with four gallons of vinegar, by the time I am done the vinegar will be half strength.

Questions:

Is it plausible the recirculation side of my hot-water plumbing is the source of the water than keeps accumulating during draining and/or flushing the WH?

If so, should I attempt to drain the recirculation pipes by opening all my hot water fixtures during the pre-flush draining phase of the process?

Is it important to have a shutoff valve installed at the recirculation line where it enters the WH? (I'm plenty annoyed this wasn't done when the WH was installed, given that the installation manual shows a shutoff valve on that line.)

Am I making too much of this? Will the vinegar do its work in the first few minutes of the flush, before it becomes significantly diluted?

Thanks.

 

[John Gayewski]

You should not dilute the descaling solution.

Yes you need a valve on the recirculation line.

Try shutting the water service to the house off and opening all of the fixtures to drain all of the water lines. To down draining you could blow air through a hose bib or any stop at fixtures. While you're doing this add a valve for the recirc. Then descale and refill.

 

[Mulligan7]

I greatly appreciate your advice, John G. Sorry for the late reply. I just did the descaling today.

I did not install a shutoff in the recirculation line. I do think it should have one, but I wanted to see if I could successfully descale without it. I had looked at two other houses on my street (new, as yet unsold), and neither of them has a shutoff on the recirculation line. Maybe I'm being too generous, but I doubt the plumbing contractor would install tankless water heaters in a way that makes it impossible to properly descale them.

As you recommended, I shut off the house's water service, which stopped the flow I described in my earlier post. So, I take it that a little water passes through single-lever faucet valves from the cold side to the hot side even when the valve is in the closed position. I can't think of any other way water from the cold side could get to the hot side of the plumbing when the water heater is shut out of the system.

During the descaling (about 70 minutes) the water level in the bucket did not change. When I was done, I ran water from the hot taps for several minutes and didn't detect any vinegar smell. So, I'm fairly confident no fluid entered or exited the recirculation lines in the house during the descaling.