Is this a water hammer?

[Squeak]

I have recently started hearing a new banging sound coming from my tankless water heater, mostly when toilets stop filling, and when my wife is quick to turn off and on the kitchen faucet.

Unfortunately, the heater is right under our master bedroom, so in the mornings, the banging sounds wake me up (poor me! )

My son and I went exploring tonight to try and see if we can figure it out, and we can hear the sounds best coming from inside the tankless heater. I took off the cover and took the video below.

My son is at the basement sink, and turning on the cold water quickly, and then shutting it off quickly (which causes the bang and echo).

I also know that it happens inside the heater because when I shutoff the cold water isolation valve at the heater, the noise stops almost 100% (you can hear real faint, but nothing like this). Odd enough, shutting off a 1/4 turn valve I have earlier in the cold water line right before the check valve did not stop it.

I tried putting on one of the AA sized water arrestors right where the basement sink connects in to see if it was a water hammer, but that did not change it at all.

Is this a classic water hammer issue, and by putting a on a larger whole house water arrestor (like from Sharkbite), it will solve it?

Tankless is on the last stop of the cold water run for the house, if that helps at all.

 

[Esobocinski]

No. Water hammer is when water is flowing and then suddenly stops when a valve closes quickly. Your problem is during heating when water isn't flowing. My first guess is that you have some mineral buildup in the heater that is causing knocking, but I don't know tankless heaters very well, so there might be another reason.

If it actually was water hammer, that AA-sized arrester would have solved it. A residential system doesn't often need anything larger.

 

[Sponsor]

 

[hj]

A "knocking" water heater is caused by water turning to steam and then violently condensing back to water. It is caused by mineral buildup in the heater's coil which prevents the water from flowing fast enough to NOT overheat. You either have to reduce the flame size or "delime" the coil, (which is a normal maintenance process anyway and should be done at least yearly). It is NOT water hammer and arrestors will not help, especially NOT a "whole house" arrestor which are normally NEVER effective.

 

[Squeak]

No. Water hammer is when water is flowing and then suddenly stops when a valve closes quickly. Your problem is during heating when water isn't flowing. My first guess is that you have some mineral buildup in the heater that is causing knocking, but I don't know tankless heaters very well, so there might be another reason.

If it actually was water hammer, that AA-sized arrester would have solved it. A residential system doesn't often need anything larger.

A "knocking" water heater is caused by water turning to steam and then violently condensing back to water. It is caused by mineral buildup in the heater's coil which prevents the water from flowing fast enough to NOT overheat. You either have to reduce the flame size or "delime" the coil, (which is a normal maintenance process anyway and should be done at least yearly). It is NOT water hammer and arrestors will not help, especially NOT a "whole house" arrestor which are normally NEVER effective.

Sorry, I should have been clearer. A couple of things:

1) This tankless is brand new -- installed in December. I can't imagine there is mineral buildup already
2) The noise only happens when the faucet is turned off very quickly, or opened very quickly. Normal usage it does not seem to create the sound. What you are hearing in the video is my son turning on the faucet, and then quickly shutting it off (and then the sound happens)

 

[WorthFlorida]

I'd call the company that made the heater or the plumber that installed it. It may be a know issue. Maybe inside the heating chamber a pipe within it is moving ever so slightly and its hitting something? There might be an anti backflow valve that is opening and closing? The weird thing is you hear it with the cold water being turned off with no water running through the heater. Sounds like (to me) something inside the heater is moving when the water pressure changes. If no fix can be found an expansion tank on the cold water side may take care of it. All guess at this time.

 

[Squeak]

I'd call the company that made the heater or the plumber that installed it. It may be a know issue. Maybe inside the heating chamber a pipe within it is moving ever so slightly and its hitting something? There might be an anti backflow valve that is opening and closing? The weird thing is you hear it with the cold water being turned off with no water running through the heater. Sounds like (to me) something inside the heater is moving when the water pressure changes. If no fix can be found an expansion tank on the cold water side may take care of it. All guess at this time.

I agree, it is really weird that it happens when cold water is being run (you can hear it very slightly when the hot water is run), which is why I assumed it was the same principle as a water hammer (pressure waves causing the the noise).

Oh, and there already is an expansion tank on the cold water line.

 

[WorthFlorida]

For what its worth check the expansion tank that it is not water logged. Hammer noises that I've heard is usually a continuous noise and it slowly dissipates. The shock wave bounces back and forth (an oscillation) for a several seconds. When water is abruptly turn off any loose hanging pipes will rattle some but that is not what you have.
Open up two faucets with the cold water running, then turn off one if them and see if the noise happens. The faucet that is running see if the water is coming out in a steady stream or seems to pulse out and does the noise continues. You still need to call the manufacture of this unit and run it by them.
.

 

[Squeak]

For what its worth check the expansion tank that it is not water logged. Hammer noises that I've heard is usually a continuous noise and it slowly dissipates. The shock wave bounces back and forth (an oscillation) for a several seconds. When water is abruptly turn off any loose hanging pipes will rattle some but that is not what you have.
Open up two faucets with the cold water running, then turn off one if them and see if the noise happens. The faucet that is running see if the water is coming out in a steady stream or seems to pulse out and does the noise continues. You still need to call the manufacture of this unit and run it by them.
.

I love this forum. This is the second time now where posting a problem, someone gives me an insight that pushes me in the right direction, and appears to fix my problem.

Your thought on the expansion tank might be right. With the water off at the expansion tank, it only read 30psi at the valve. House water pressure is 60psi. Went and bought an air inflator (always a good excuse to buy new tools! ) pumped it back up to 60psi, turned the water back on, and did our test, and I don't hear it as loud any more.

With the cover off the tankless, I can hear slight water movement when the quick closing valves shut down, but not the banging at all. I won't claim victory yet until I get through our typical 24-hour cycle (especially morning with my wife), but things look real positive.

My theory: when the plumber installed the new tankless, he just moved over my old expansion tank. It probably lost pressure in that process, and he didn't think/remember to recharge it back up.

Thanks again for the insight.

 

[Jadnashua]

FWIW, moving an ET won't discharge it, but like a car tire, eventually, it does lose a bit of air...IOW, they do need to be checked once in awhile. Note, the water supply must be off and a valve open before you can accurately adjust the air pressure in an ET. The bladder must move freely to precharge it, otherwise, you're trying to compress water, and that doesn't' work - the pressure will go up, but the static position of the bladder won't be in the right place.

 

[Squeak]

FWIW, moving an ET won't discharge it, but like a car tire, eventually, it does lose a bit of air...IOW, they do need to be checked once in awhile. Note, the water supply must be off and a valve open before you can accurately adjust the air pressure in an ET. The bladder must move freely to precharge it, otherwise, you're trying to compress water, and that doesn't' work - the pressure will go up, but the static position of the bladder won't be in the right place.

Ahh, yeah, that makes sense about it not discharging it while moving it. The ET was about 7 years old, so natural bleed off, I guess.

And yes, the water supply was turned off. I have a shutoff valve for the cold water going into the tankless, right before the ET. Turned that off, shut the valve on the hot side of the tankless, and then released the water pressure by opening up the isolation valve on the cold side (with a hose hooked up to it). Bunch of water came out, and then nothing.

Only then did I measure (30psi) and fill. FYI, it was measuring 50si when under water pressure before I did all of this.

 

[Jadnashua]

Until you release the water pressure, the air pressure in the ET is exactly the same as your water supply pressure and gives you a fairly easy way to check it if you don't have a water pressure gauge.