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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