Troubleshoot no-flow flushing of Navien NPE-A240A2

[Jughead135]

I have a pair of Navien NPE-240A2 tankless heaters. For reasons known only to my home's builder, there are no recirc lines in the house, so only the internal recirc is functional.

As I attempted to flush them, I got no flow at all when I tried the first one. Hooked up to the second one, everything worked normally (so, it's not my pump or my hookup skills! ).

I tried reversing the flow, no dice--though, this time, the pump ran for a while longer w/ water flow & the bucket level dropped (none coming out of the discharge) before reaching equilibrium. When I turned the pump off, there was a clear sound of water draining & the bucket returned to its previous level. I assume that means I filled (then drained) the internal tank--but, still no flow through the exchanger.

My only guess is there's something wonky with the check valve for the recirculation, and the pump ends up fighting itself but the pressure has nowhere to go?? Other thoughts? What's my next move? Thanks for any pointers!

 

[Fitter30]

Turn the supply water on see if it fills the bucket with hot water cleaning valve open. Then with a clothwasher machine hose try to flush backwards with garden hose . Close supply off and open cleaning valve open.
E016 or EO30 fault code?

 

[Sponsor]

 

[GReynolds929]

You most likely need a new water adjustment valve.

 

[Jughead135]

Turn the supply water on see if it fills the bucket with hot water cleaning valve open. Then with a clothwasher machine hose try to flush backwards with garden hose . Close supply off and open cleaning valve open.
E016 or EO30 fault code?

Thanks! I had done the cold-side yesterday, it didn't occur to me to try the garden house "backwards." In any case, I set up to do your test today. The cold-side flush with system pressure worked normally. Just to be thorough, I tried the pump again...

...and I got a trickle. Not much, but more than the "nada" that I saw yesterday. After a bit (15 seconds or so?), it noticably increased in flow. At about a minute total later, flow was up to normal. I left the pump running for 60 minutes, all seemed to work normally from that point forward, and the heater appears to be working normally afterward. Fair amount of crap came out of the filter (which I know wasn't there by the time I cried "Uncle!" yesterday, because I had the filters out to clean as an early troubleshooting step) and in the bottom of the bucket--hard to say if that was on a valve somewhere or what.

No error codes at all.

So, am I out of the woods here? Or is something damaged or worn & I just got a temporary reprieve?
Thanks so much for the help!

 

[Jughead135]

You most likely need a new water adjustment valve.

Do you still think so, given my experience posted to @Fitter30 above?

I appreciate the response & help!

 

[Fitter30]

Thanks! I had done the cold-side yesterday, it didn't occur to me to try the garden house "backwards." In any case, I set up to do your test today. The cold-side flush with system pressure worked normally. Just to be thorough, I tried the pump again...

...and I got a trickle. Not much, but more than the "nada" that I saw yesterday. After a bit (15 seconds or so?), it noticably increased in flow. At about a minute total later, flow was up to normal. I left the pump running for 60 minutes, all seemed to work normally from that point forward, and the heater appears to be working normally afterward. Fair amount of crap came out of the filter (which I know wasn't there by the time I cried "Uncle!" yesterday, because I had the filters out to clean as an early troubleshooting step) and in the bottom of the bucket--hard to say if that was on a valve somewhere or what.

No error codes at all.

So, am I out of the woods here? Or is something damaged or worn & I just got a temporary reprieve?
Thanks so much for the help!

Just keep up with yearly maintenance. Make a note of flows between heaters turn a bath and shower full hot write down gpm flows. Then there's something for comparison.