Navien tankless banging

[fittan]

Hi I just moved into new place with Navien NPE-240A. Whenever I start the washing machine the Navien makes a really loud banging noise (see link below).

I tried installing water arrestors on both the hot and cold valves at the washer but it didn’t help. The tankless works fine for showers and faucet. Any ideas thanks.

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[Breplum]

That is some weird banging. Sorry, I've never encountered anything like that.
First, I would run the hot hose from the WM tap into a sink or bucket or outside to see if it is coming from the hose bibb tap.
2nd, I have been a grimy plumber for decades and high efficiency laundry detergents in HE WMs do not need hot water whatsoever. We get incredibly clean clothes with cold water even the most grimy work clothes using only cold water.

 

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[John Gayewski]

Is the sound coming from the water heater or the piping.

 

[fittan]

It’s from the Navien tankless. When it happens the GPM on the display fluctuates from 0 to 3 GPM.

 

[John Gayewski]

It’s from the Navien tankless. When it happens the GPM on the display fluctuates from 0 to 3 GPM.

I would try adding an expansion tank if you don't have one.

 

[royalflush001]

Ensure that your home's water pressure is within the recommended range for the Navien NPE-240A. Also, in addition to the water arrestor, install a water hammer arrestor on other appliances or fixtures connected to the plumbing system. I hope this might help.