Rinnai Humming

[johnmsch]

I have a 12 year old Rinnai R94-LSi tankless water heater that has recently started humming. This only happens when first turning on the hot water in a shower at the far end of the house and stops after about 30-45 seconds. I wouldn't think its any kind of build-up in the pipes in the unit, as I do the vinegar flush once a year in the first week of December. I also have a whole-house water filter on the water line coming into the house.

Any ideas on what could be causing this?

 

[breplum]

How hard is your water and how long do you descale for normally?
you might want to try one of the commercial descaler solutions or even CLR and run pump for an hour.

 

[Jeff Handy]

It was humming because it couldn’t remember the words.

 

[johnmsch]

How hard is your water and how long do you descale for normally?
you might want to try one of the commercial descaler solutions or even CLR and run pump for an hour.

Thanks for the reply.
I'm in Cobb county Georgia and we always have one of the highest rated water systems in the US. Hard water is definitely not an issue.
I always run the white vinegar flush for a full hour. I'm a bit skittish about using anything other than what is recommended by Rinnai. It says either white vinegar or some kind of a citrus solution. Never really looked into that citrus option to see what is available.
Do you have any personal experience using commercial descalers?

 

[johnmsch]

It was humming because it couldn’t remember the words.

Too funny! I really needed a good laugh like that.

 

[breplum]

I use the commercial tankless descale solutions all the time.
The only solutions made for tankless descale are "non-toxic", plus you clear water flush thouroughly after running the solution through.
I don't know why Rinnai is so insistent about white vinegar and paranoid about any normal solution, when other mfrs don't have issues.

 

[johnmsch]

I use the commercial tankless descale solutions all the time.
The only solutions made for tankless descale are "non-toxic", plus you clear water flush thouroughly after running the solution through.
I don't know why Rinnai is so insistent about white vinegar and paranoid about any normal solution, when other mfrs don't have issues.

Thank you sir. I'll start looking into this option.

 

[Jeff Handy]

I have limited knowledge of tankless, but see if yours has any filters or screens up or down stream that might need cleaning or changing.

Just a thought.

Humming noise is often causing by a choke point.

Or by a worn valve, or a loose washer or gasket vibrating.

 

[johnmsch]

Thanks for all the replies and the fix is really strange.
I occasionally have to take the fan out of the unit and clean it with compressed air when one of those helicopter leaves gets sucked into the air intake and jams the fan, throwing an error code 61. Last time I did this was last spring. Evidently, I didn't fully seat the rubber boot that connects the fan to the air intake. It had come completely off the fan. Once I put it back on and re-seated the spring clamp, the noise has gone.
I absolutely don't understand how this would have caused the loud humming, but its now gone away.