Weird consistent pipe knocking noise even when everything is off and valves closed

mzhou184

I recently moved into a high rise building condo(36 floors) and within the first night I noticed a consistent knocking noise in the wall that is more frequent during early mornings and late nights, it is very noticeable and can be heard anywhere in the entire unit, it is driving my wife and I crazy and we would wake up at 3-4am in the morning because of it. We can't go to sleep without ear plugs now.

My building has a central boiler in the top floor and sends hot water to each floor/unit, the hot waster runs through the fan coil unit in each unit zone and output hot air. It flows in the following direction: Central Boiler-->Building Zone Main pipe that goes through floors(wrapped with rubber insulation) -->flow control ball valve of my unit(it is right by the building main pipe)--> zone valve actuator -->fan coil unit. No hidden pipe is unaccounted for here.

I opened up my air handling unit/fan coil unit cover and learned that the noise came from the hot supply valve and pipe going to the fan coil unit and I can feel the vibration in the pipe when the sound goes off . We have a four pipe system with 1 hot supply line/1 hot return line and 1 cold supply line /1 cold return line, the only pipe that vibrates when the sound goes off is the hot supply line, nothing on the other three. I asked my property manager and building engineer if my neighbors had the same complaint and apparently nothing had been reported, and if there is air in the pipes, everyone would hear it. This rules out the Building zone main pipe from the problem.

Please see the video I uploaded on Youtube documenting the sound:
https://www.youtube.com/watch?v=U1fetqBqwu4


I tried to troubleshoot on what might be the cause:

1. Turned off Nest Thermostat, noise persists
2. Turned off fan coil unit, noise persists
3. Turned off all the power in the entire unit (switched off breaker box main), noise persists
4. Manually closed the flow control ball valve of hot supply line, noise persists
5. Manually closed the flow control ball valve of all the pipes, noise persists

As mentioned before, the vibration can only be felt on the hot supply line as the sound goes off, this leads me to believe it might be the ball valve (valve that controls flow of water from building main pipe to our unit's fan coil unit) failing that's causing this noise because the noise kept going even after powering off everything and regardless of opening/closing the valve.

I hired a HVAC technician to take a look and he checked over everything including the zone valve actuator to make sure it was opening/closing as intended and it was. He arrived the same conclusion as me: faulty ball valve because nothing else seems to be the culprit, but before deciding to change the valve I wanted to make sure this is indeed the issue because changing the valve requires draining the pipe of the entire building, that's a lot of water we are talking about and we'd have an entire building without heat for a couple hours.

Thanks for the help!

EdTheHeaterMan

I'm afraid that does not sound like a defective ball valve. It sounds like a pipe that is in the wall somewhere. As copper pipes change the temperature the metal expands on an increase in temperature and the copper will contract as the temperature is reduced.

There is one other possibility. There may be a motorized valve that is trying to close and the last gear on the motor is worn. As the motor continues to turn to make that final stop, the gear slips and makes that noise. As the motor continues to turn, it continues to hit that bad tooth in the gear. If the gear was not damaged the motor would completely close the valve and activate a microswitch and the motor would stop.

If it is piping expansion, It will be difficult to find where the pipe is rubbing. if it is a valve actuator it might be on the cooling water actuator and somehow the noise is transferred to the heat supply pipe. Try this... turn on the cooling system to see if that valve actuator stops the noise. (i assume you only operated the heating side)

I hope this helps, but I'm not confident it will

Respectfully submitted
Mr.Ed

EdTheHeaterMan

I have another story about a rattling noise in my car. When I took it to a mechanic to see if he could fix whatever was making the noise... he turned up the radio louder. Then said "Fixed!"

Not so funny but you get the point. Perhaps that banging/tapping needs some white noise to mask it until you get used to it. I don't hear my refrigerator anymore but when I first moved in here the ice maker valve and the crash of the cubes hitting the bin were enough to drive me to drink. So I would get some of my newly manufactured ice cubes and add them to a glass of Scotch. Then I would say "Alexa, White Noise" and all was good in the world. I've been here about 4 months and I don't even know I have a refrigerator.

I guess 8 bottles of Scotch will do that to you.

mzhou184

Hi Mr. Ed, thanks for replying to me.

The Building Main pipe is immediately next to the ball valve with a T-connector (wrapped with rubber insulation) so there is no other pipe or anything that would rub against and the ball valve down stream pipe is short and all visible and goes into the fan coil unit with a zone valve actuator in the middle controlling the open/close for the fan coil unit, I think this would eliminate pipe expansion from the issue.

As for the zone valve actuator, the noise persists even after powering down the entire unit, would the motor on the zone valve continuing try to turn without power?

The noise is very audible and quiet loud, can be heard in the entire unit, impossible to drown with a white noise machine and it goes off every couple seconds sometimes, and other times it would go off every 30-50 seconds.

thanks again!

hot_rod

the noise could be coming from another unit, copper pipe will telegraph the noise throughout the building. See if the neighbors hear the same noise.

hot_rod

looks like a two wire zone valve below the manual valves, could the noise be coming from that?
Sometimes they use NO, normally open zone valves, so it would be powered when the T-stat is off and could have the gear issue @EdTheHeaterMan mentioned. Disconnect one of the leads see if that changes anything.

EBEBRATT-Ed

@mzhou184

Try what @hot_rod said. Sometimes in heating /ccooling systems the valves are wired to "fail open'. That is so if the valve fails the space will overheat ....better than freezing!!! But if the actuator is failing the valve being powered all the time when the heat is of it could be clicking or making noise.

Also, check to see if the valve is installed correctly in the direction of flow. Their should be an arrow or some markings like "AB and B" or something on the valve.

Especially in a large building with a 4 pipe system it is easy to get confused and install a valve backwards

EdTheHeaterMan

mzhou184 said:

Hi Mr. Ed, thanks for replying to me.

The Building Main pipe is immediately next to the ball valve with a T-connector (wrapped with rubber insulation) so there is no other pipe or anything that would rub against and the ball valve downstream pipe is short and all visible and goes into the fan coil unit with a zone valve actuator in the middle controlling the open/close for the fan coil unit, I think this would eliminate pipe expansion from the issue.
!

You are making the assumption that the only pipe that expands and contracts is the short one in your apartment. The expansion could be the large pipe (with the Tee) that your unit is connected to... and it could be rubbing on a stud, joist, or support inside the wall near the floor or ceiling. Just because you hear a noise in one place does not make it the source of the noise. Acoustics is a very complicated science. I hope you are correct about replacing the noisy part. I would not want to be the contractor who is going to do that job only to find that the part replaced was not the source of the noise.

I would want to get paid for replacing the valve you told me to replace even if it did not solve the problem. As a customer, I would not want to pay for some expensive project and not get the desired result. "Catch 22" and you are both entitled to your opinions, but the worker still needs to be paid.

I wish you the best in resolving your issue.

Mr.Ed

mzhou184

EdTheHeaterMan said:

mzhou184 said:

Hi Mr. Ed, thanks for replying to me.

The Building Main pipe is immediately next to the ball valve with a T-connector (wrapped with rubber insulation) so there is no other pipe or anything that would rub against and the ball valve downstream pipe is short and all visible and goes into the fan coil unit with a zone valve actuator in the middle controlling the open/close for the fan coil unit, I think this would eliminate pipe expansion from the issue.
!

You are making the assumption that the only pipe that expands and contracts is the short one in your apartment. The expansion could be the large pipe (with the Tee) that your unit is connected to... and it could be rubbing on a stud, joist, or support inside the wall near the floor or ceiling. Just because you hear a noise in one place does not make it the source of the noise. Acoustics is a very complicated science. I hope you are correct about replacing the noisy part. I would not want to be the contractor who is going to do that job only to find that the part replaced was not the source of the noise.

I would want to get paid for replacing the valve you told me to replace even if it did not solve the problem. As a customer, I would not want to pay for some expensive project and not get the desired result. "Catch 22" and you are both entitled to your opinions, but the worker still needs to be paid.

I wish you the best in resolving your issue.

Mr.Ed

The large building pipe is wrapped with thick rubber insulation throughout the floors/building, they are not exposed that's why I thought expansion /contraction might not be the issue.

mzhou184

hot_rod said:

looks like a two wire zone valve below the manual valves, could the noise be coming from that?
Sometimes they use NO, normally open zone valves, so it would be powered when the T-stat is off and could have the gear issue @EdTheHeaterMan mentioned. Disconnect one of the leads see if that changes anything.

I did disconnect both of them and turned everything off and even turned the breaker box main switch off, the noise was still there...

mzhou184

EBEBRATT-Ed said:

@mzhou184


Also, check to see if the valve is installed correctly in the direction of flow. Their should be an arrow or some markings like "AB and B" or something on the valve.

Especially in a large building with a 4 pipe system it is easy to get confused and install a valve backwards

if that's the case, wouldn't turning off the ball valve stop the flow and that should end the noise? but the noise is still there with all the power in the condo switched off and all the ball valves closed.

Apparently my other zone is also having the same issue but a lot less frequent. My hvac technician now thinks the sound comes from the boiler and the entire system needs to be flushed, but again, if that were the case wouldn't my neighbors also have the same problem? I was told by my building engineer that this particular issue I have is an isolated incident... I am really running out of ideas on what might be the cause.

aperson

That noise is a super drag. I've recently had a boiler repair fiasco that got air into my heating pipes. Trapped air seems to be able to mimic all kinds of other reasons. Such as copper expanding. Why would it be expanding in only one spot. In my situation that is a spot that never made noise before. Does the noise ever go away? If it is happening when the whole system is dead cold it is not a bubble or contraction of metal or contraction of bubble. 

EdTheHeaterMan

This post makes me believe that the noise has nothing to do with the equipment in your unit. That noise is telegraphing from the main. Somewhere else in the system on that main pipe, the temperature is changing a few degrees hotter as the boiler fires up, then the boiler reaches the high limit and the temperature of that main pipe decreases slowly. If the noise stops for a few minutes, that is the point in time between cycles where the water temperature is neither increasing nor decreasing for a minute or so.

As the temperature is changing the main pipe is expanding or contracting. That movement of the main pipe may be rubbing on something inside the wall near your equipment. That is a tough thing to find.

You mentioned you recently moved in... Is this a property that you own or a property that you rent? If it is a rental, you may want to start looking for someplace else when your lease is up. (or was the price too good to be true?)

mzhou184

EdTheHeaterMan said:

This post makes me believe that the noise has nothing to do with the equipment in your unit. That noise is telegraphing from the main. Somewhere else in the system on that main pipe, the temperature is changing a few degrees hotter as the boiler fires up, then the boiler reaches the high limit and the temperature of that main pipe decreases slowly. If the noise stops for a few minutes, that is the point in time between cycles where the water temperature is neither increasing nor decreasing for a minute or so.

As the temperature is changing the main pipe is expanding or contracting. That movement of the main pipe may be rubbing on something inside the wall near your equipment. That is a tough thing to find.

You mentioned you recently moved in... Is this a property that you own or a property that you rent? If it is a rental, you may want to start looking for someplace else when your lease is up. (or was the price too good to be true?)

Unfortunately we just purchased this property, we asked the previous owners to see if they ever experienced such noise they said no, we asked the building management and engineer they also said they never received complaint about it and the previous owner was a board member of the HOA, she would have made it known to them had she experienced something like this. The previous owners moved out around last October and the condo unit was vacant until we purchased it early March.

One interesting thing I noticed is that if I turn the heat all the way up to 80 degrees, the noise is almost non existent after it runs for a bit and while it keeps running. If it's pipe thermal expansion, wouldn't higher temp make it worse?

Do you think it's due to sediments /debris around the T connector between the main pipe and the ball valve because the heating unit was not running as much and therefore water was not moving when the condo was vacant?

aperson

Here are my thoughts. I am no expert. If you turn up the heat and thereby increase the psi, because hot water is expanded water, bubbles would dissolve or contract under pressure. And, stop causing noise. Also metal can only expand so much. My copper pipes make no expansion noise. Truthfully, I think this is just a catch all rationale. Sure air might have seeped in there while it was vacant and now you have a stuck bubble. I sincerely hope I am not projecting my bubble issues.

EdTheHeaterMan

aperson said:

Here are my thoughts. I am no expert. If you turn up the heat and thereby increase the psi, because hot water is expanded water, bubbles would dissolve or contract under pressure. And, stop causing noise. Also metal can only expand so much. My copper pipes make no expansion noise. Truthfully, I think this is just a catch all rationale. Sure air might have seeped in there while it was vacant and now you have a stuck bubble. I sincerely hope I am not projecting my bubble issues.

I don't see the science in this statement. If the pressure increases at any given point in a closed system, as a result of a temperature increase, the entire system pressure will increase.

Unless you write what pressure you want the water to be inside the pipe, the water won't be able to see it. so the water will go from high pressure to low pressure until it is equal.

And how does the air that "seeping" know if a place is vacant or occupied?

This Air must be pretty sneaky. Waiting until the place is vacant to sneak in seeping and slithering while no one is there to fight it off. What kind of neighborhood is this, anyway?

Have you notified the mattress police, You know, the ones who enforce the mattress tag removal under penalty of law? I believe they also investigate Seeping Air. It's part of the Laws of Physics that aperson might be able to get around... If they know the right people

aperson

Most likely there would be a leak for air to get in.

neilc

well,
air can't get in if there's enough water pressure pushing out, or up,
and, if the circ is adding to the point of no pressure change(expansion tank) by pumping away, not into.

EdTheHeaterMan

aperson said:

Most likely there would be a leak for air to get in.

Where would the leak be that allows air in against all that pressure created by hot water? Or is that part of the Laws of Physics that aperson might be able to get around... If they know the right people?

I'm trying to picture it in my mind's eye. A leak that lets air in when a system is under pressure that is greater than the air pressure outside of the system. I'm No Expert on Physics... so learn me how that works.

aperson

A water leak, maybe between two parts, a seam, could create enough of a vacuum to allow air to displace the water. It is that or as water leaks out as it allways does, you are suggesting that the quantity of air inside the pipe remains constant while the water quantity declines. A pressure regulator is not that sensitive.

aperson

Maybe water leaks out and air can't squeeze past. The space is filled with expanding water because the loss of water reduces the pressure. Eventually the pressure regulator lets in fresh water to raise the psi. Fresh water contains air. An air bubble could still be trapped. Unless Heater Ed is right and the noise is a stuck note dropped from a traveling sound wave.

HomerJSmith

I am an expert! "X" in mathematics is "unknown" and a spurt is a drip under pressure. Pretty well fits me.

Just a thought that came into my mind. Is the noise a velocity issue with an over sized pump? How about a swing check bouncing?