Hot Water Recirculation Pump Much Louder after Pipe Repair

[Poseidon]

A pinhole leak had developed in the copper pipe that's circled in red in the attached photo.

A plumber came out and made the repair. However, that night, I noticed that our (four-year-old) Grundfos UP 15-29 SU recirculation pump was operating much more loudly than usual -- we could even hear it running throughout the house, its low whine transmitting through the pipes.

I contacted the plumber and they mentioned it's probably just "residual air" in the line that "needs to be bled."

I'm a total n00b when it comes to plumbing, so I apologize in advance if this is a super basic question: does that diagnosis sounds correct and, if it might be correct, how exactly would I go about purging the system of this "residual air?"

THANK YOU, guys!

 

[MicEd69]

As you describe the sound as a "low whine", I would guess it is the sound of the pump resonating through the piping. But I guess it could be air in the line, which will eventually work its way out of the system. The leak was right at your check valve, so damage or foreign material in it could possibly be an issue. It's just hard to say when one can only describe the sound.

How are you running your pump? 24/7? On demand? On a timer during expected hot water needs?

 

[Poseidon]

Yes -- "resonating through the piping," that's exactly what it sounds like.

The pump is on a timer -- about three hours in the morning and three hours in the evening.

It's hard to tell but the noise appears to be a bit quieter today -- perhaps air is indeed working its way out of the system, as you say...