Noritz Tankless Making LOUD noise first thing in morning - audio link included

[klaus8928]

Hello. I have a Noritz NR71-SV tankless water heater with an RC-7651M remote. It was installed about 13 years ago and still works well, except for a loud noise it has started making (see link).

Unmute/turn up volume in the imgur and your device to hear the Loud Noise .

This noise generally occurs after a long period of idleness, such as first thing in the morning. It started about a year ago, is loud enough to be heard outside, and frequently wakes people up around 5:15 AM. The noise occurs regardless of whether a hot water fixture is opened slightly or fully. Typically, it only happens once and will not reoccur throughout the day.

I descale the unit every two years. Our local water is somewhat hard, but not severely so. After a one-hour flush, there is evidence of removed scale but no rust, and the buildup is nowhere near as extreme as examples I've seen online. The home does not have a whole-house water filter or softener, but there is a properly functioning main pressure regulator.

The linked audio was recorded about one foot away from the unit. Note that this issue never occurs when a cold water source is opened.

Finally getting after this, and Noritz is closed today so thought I try here. Thanks!

 

[GReynolds929]

Is it the gas valve solenoid, or fan? Is the inlet filter clean?

 

[Sponsor]

 

[Fitter30]

Not familiar with the brand. Noise is strange. Stated that every two years you have taken care of the water side but what about the combustion air. From the fan to cleaning the HX.

 

[klaus8928]

Is it the gas valve solenoid, or fan? Is the inlet filter clean?

I'll have to look into what type of gas valve it has. I have the parts list (attached), but nothing calls out solenoid or fan. I hear a fan come on right as a hot water source opens, but I thought that might be the exhaust fan (113). You really make me look at this from a different angle now though. I had it in my mind that this noise was being generated by a water valve or manifold, but it does sound like a horn of sorts, and now I'm interested in finding more about the gas valve. Hmm. Thanks, I appreciate that.

 

[Fitter30]

Not familiar with the brand. Noise is strange. Stated that every two years you have taken care of the water side but what about the combustion air. From the fan to cleaning the HX.

 

[klaus8928]

Not familiar with the brand. Noise is strange. Stated that every two years you have taken care of the water side but what about the combustion air. From the fan to cleaning the HX.

Honestly, no servicing of the fan or cleaning the heat exchanger. Not due to laziness, just ignorance I reckon.
Much appreciate your reply. I'll look into those service items.

 

[thomasbecker]

That loud morning noise on a cold start usually points to gas regulator lockup or an air/fuel imbalance. When the unit sits overnight, static gas pressure can build up and cause a hard, vibrating ignition on the first hot water draw.

Try cleaning the air intake filter and burner assembly, check for scale buildup in the heat exchanger, and have a tech test both static and dynamic gas pressures at the inlet.

 

[Fitter30]

Lock up on a gas reg occurs when the gas flow stops and the orfice is blocked shutting off the flow. Test is putting a gauge down stream and seeing if the pressure rises. Should be a downstream tap at the reg or units gas valve. Sometimes a tee has to be cut in and gauge port would be 1/8" pipe thread. Assume this is lp?