NPE-240A2(NG) - Recirculating pump not turning on

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I hope some kind soul on here can help me.

I have a Navien tankless water heater (Model: NPE-240A2(NG)) which is a little over 2 years old. I have a dedicated return line for the recirculation.

About a week ago, I noticed that the hot water was taking over a minute to come instead of seconds. It seems as though the pump stopped turning on.

I called out a plumber who just ended up calling Navien technical support, who recommended replacing the check valve. Once the part arrived, the plumber came back out and replaced it but that did not resolve the issue.

The next guess with Navien was that the pump itself was faulty, so they sent out a replacement for that. The plumber came this morning and replaced it - but it still looks like it never turns on.

I have tried to put the recirculation pump in test mode to force it to start, and I can hear some clicking noises - but the pump does not turn on.

There are no system error codes. All settings have been verified (external circulation line, valve in correct position, no external pump connected). And also tried to do a factory reset in case it is a software related issue.

My next guesses are 1) replace the PCB , or 2) it's something to do with power not reaching the pump. I am leaning towards #2 since I hear clicking noises when the pump is in test mode which makes me think a signal is being sent properly from the PCB.

Does anyone else have a guess on what might be going on and how I can narrow it down? If it is a power failure, how would I go about testing for that?

At this point, I'd prefer to order the parts out of pocket and do the labor myself rather than have the plumber come out for the 4th time.. Unfortunately, Navien will not be send me as a non licensed person the parts :(

Thank you!


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If you have a multimeter you can unplug the pump connector from the PCB and measure the voltage at the PCB contacts. There should be between 96v-138v. Did the new pump have the air purged when it was installed? Is the three way valve set to external? What does the error history show?


Licensed plumbing contractor
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San Francisco Bay Area
Ultimately, if you can't troubleshoot on your own, only call a Navien Service Specialist listed company (NSS). They are required to have a nearly full parts kit and should be much more knowledgeable about not leaving you without specifically solving the problem (as long as it is not something in your house piping for some strange reason).
When at the unit, it can be run through tests to check so many issues. Should be able to see the gpm at will.
There were plenty of actually-bad main control boards early on when thge A2 came out but of the many I saw, the display actually said 'replace' or 'bad' (I forgot)
Hey, wait a minute.

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