Home>Discussions>PLUMBING>tankless water heater noises
6 posts / 0 new
Last post
tankless water heater noises

I recently plumbed in a new Noritz tankless heater. Besides having the typical "takes a while to get hot water issues", mine also makes a "long horn" sound upon start up and than again when the faucet shuts off. I haven't had the chance to contact tech support as I haven't been able to get somebody to turn on the water in the house while I sit with the phone outside with tech support. The horn sound is a bit annoying, but what's even odder is when I flush the toilet, I hear the horn sound after the flush is over. The toilet is connected to cold but is there any way that a low flow toilet pulls enough cold water from the house pipes that the cold feeding the tankless sets it off? The tankless should only be sensing flow needed from the hot side right?

Thanks for helping with this quirk.

Re: tankless water heater noises

I worked with a Rheem but the idea is the same, just with another brand name. It is gas or electric? not that is should make much difference, but, when the tankless kicks on it should create the "horn" sound, but not enough that you would hear inside your home. Really, the only thing I can think of is that the water being pulled through your water supply lines is creating a negative void in the supply and the sound might be the same as if you inhaled through your lips and whistled. the same with the water pipes. the reason it goes away in the middle of operation of the facet is the demad equalizes and is being meet.

So call Noritz, get a tech out there and check the sizing of the water pipes. Make sure the water isn't being "stolen" from the tankless when you flush a toilet (a check valve would fix that).
And good luck. Process of Elimination.

Re: tankless water heater noises

Misfitter, thanks for the reply.

I have yet to call tech support as I'm never home when they are available.

Anyway, I think you're right with regards to the toilet making the heater go. I shut off the water going into the tankless and flushed the toilet and didn't get the horn sound. I'll throw in a check valve when I get around to doing some plumbing next.

The sound is definitely a horn and I think it must be transmitting louder than expected into our house, through 80 year old studs and uninsulated walls. I'm also adding on to the house right now so some adjacent walls are completely stripped down as well.

Apart from the check valve issue, these noises seem like a normal phenomenon for these units. Hopefuly most of it gets damped when our house closes up.

Re: tankless water heater noises

Do you also have an expansion tank on the down strean side of the unit? This will allow "extra pressure/water" to be in the water line and may also help in the demand of water issue.

While your walls are open it never hurts to secure (or strap) them to the studs to prevent them from moving (or banging) around. Code varies, but I go with every 4' or so. If it is PEX go with 3' or so. Good luck. Process of elimination.

Re: tankless water heater noises


This sounds like a classic case of a "cross connection" and back-siphoning of water in the toilet tank due to a worn ballcock valve, another possibility is a defective washer in one of the faucets.

The ballcock valve (or similar water inlet valve) in the toilet usually has a neophrene washer/vacuum break that gets worn over time & will make loud, "longhorn" or "foghorn" sounds.

You can check this by completely shutting off the water supply valve temporarily at the base of the toilet & seeing if the noise abates when you open the kitchen faucets.

As noted, a check valve will help, but code requires that an anti-siphoning water inlet valve like a Fluidmaster 400A series be installed in the toilet tank, if the toilet valve turns out to be the problem.

Also check to see that the toilet on/off valve is completely open if there is no siphoning.


Re: tankless water heater noises

Thanks for the advice. No expansion tank installed downstream and I've got my pipes secured every 3 feet or so and have also used plastic hole bushings for going through wood.

I think the toilet stealing water issue will be eliminated with the check valve.

I still have yet to call tech support. As you can see, it doesn't bother me that much.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.