I also hear knocking, banging noises in my sinks when running hot or cold water and in my toilets when I flush. The more water I run the more knocks I hear. It has progressively gotten louder over time, and does not matter if the water is hot or cold, or if the room is hot or cold. It only started doing this recently, why wouldit start of the blue now?

Please be aware a loose washer in one of your faucets can create a hammer like sound remember water pressure is generally around 60lbs of pressure. The washer does not necessarily need to be at the faucet you turn on and off when you hear this banging

Is there a PRV ( pressure reducing valve) installed? Back to you. Tom

I am not sure if there is a PRV, I have three toilets and 4 bathroom sinks. The knocking sound is not loud at the sinks but comes from a location in the middle of the house (three level house) and also on the bottom floor if I use the sink on the bottom floor. I am now also hearing the knocking when I use the washing machine (sound occurs on the bottom floor, machine is on the second floor) but it is not as loud yet.

How many PRV's would I have (for example: a main one on the water heater or at each faucet?).

Please be aware a loose washer in one of your faucets can create a hammer like sound remember water pressure is generally around 60lbs of pressure. the washer does not necessarily need to be at the faucet you turn on and off when you hear this banging

I forgot to note the sound is coming from the middle of the house when the sinks are in use, not at the sink location - would that change your recommendation?

The PRV's located where the water enters your house. Do you have one? Back to you, Tom

Sorry Tom, had to go out of town. Yes, I found the PRV. My concern is not necessarily when the water pressure is running but when the water is draining. For example, if I run the sinks where I hear knocking, but put the stopper up it does not make a sound. I can fill the sink and no noise.

If I turn the water off. Then drain the water, I will hear the knocking within a few seconds. This leads me to think it isn't a washer, and probably isn't too high of a pressure on the PRV - but maybe I am completely wrong.

Please advise.

Do you have an AAV on that drain line?

Do you have an AAV on that drain line?

What does AAV stand for? Not sure, I owned the home for about a year and a half (before the sound starting occurring). The plumbing was new when I moved in.

AAV, Automatic Air Valve, usually used on retro fit plumbing or additions where venting of the drain lines is either not possible or difficult.

They are a mechanical means of letting air into the drain so that traps are not syphoned dry.

Being mechanical are subject to failure. Could be making a noise as they open or close.

AAV, Automatic Air Valve, usually used on retro fit plumbing or additions where venting of the drain lines is either not possible or difficult.

They are a mechanical means of letting air into the drain so that traps are not syphoned dry.

Being mechanical are subject to failure. Could be making a noise as they open or close.

OK, where would that be placed in the system? I can look for it.

Because AAV are mechanical and have to be serviced (replaced) they
Have to be exposed. Look on drain line under sink. Not to say that sometimes people don't bury them in the wall.

Also not approved for venting toilets. If you are getting noise when flushing that would make me think there is an AAV somewhere and that the toilet vent is also blocked.

The source of a sound in pipes can be very deceiving. The fact that the noise appears to be coming from the center of the house is probably deceptive. Sound is vibration. When you hear the noise, put your hand on the pipe. The stronger the vibration the closer you are to the source.

I turn the water off. Then drain the water, I will hear the knocking within a few seconds. OK! That knocks water pressure of water hammer out of the running. What I think you hear is the sink venting through the trap. That would point to a blocked vent. Try snaking it and I'll bet your noise goes bye-bye. Good luck, Tom

OK! That knocks water pressure of water hammer out of the running. What I think you hear is the sink venting through the trap. That would point to a blocked vent. Try snaking it and I'll bet your noise goes bye-bye. Good luck, Tom

OK, thank you very much for the feedback. If I understand this correctly, the block could be anywhere since the sound may not indicate the location correct? So to snake I guess I should start where I noticed the problem first on the top floor..

Also, another reader commented that I should look for the AAVs, I do not believe I have them because my venting stack goes straight up through the roof. Would I or should I have both the venting stack and AAVs?

Because AAV are mechanical and have to be serviced (replaced) they
have to be exposed. Look on drain line under sink. Not to say that sometimes people don't bury them in the wall.

Also not approved for venting toilets. If you are getting noise when flushing that would make me think there is an AAV somewhere and that the toilet vent is also blocked.

The source of a sound in pipes can be very deceiving. The fact that the noise appears to be coming from the center of the house is probably deceptive. Sound is vibration. When you hear the noise, put your hand on the pipe. The stronger the vibration the closer you are to the source.

OK, thank you. I don't see the AAVs but will look again. Where would the toilet vent be located? I have two vent stacks I believe that go straight up through the roof. Also, should those vent stacks be capped, neither one has one at the present time...

should I have both the venting stack and AAVs?No! The AAV replaces a vent through the roof. You put the problem squarely in drainage when you said,


I turn the water off. Then drain the water, I will hear the knocking within a few seconds. Does the noise come from any of your drains? You have to localize it before we can help. Back to you, Tom

No! The AAV replaces a vent through the roof. You put the problem squarely in drainage when you said,
Does the noise come from any of your drains? You have to localize it before we can help. Back to you, Tom

Not directly from the drain, I hear the noise in two places at the center of the house, one on the second floor and one at the basement/first floor floorline. Here's the play by play: I plug the drain, fill the entire sink with water, turn off sink, release the plunger and within a minute will hear the knock from the center of the house. It happens every time. It happens when I run the water without the drain plugged (as water runs through the drains I hear a knock). It doesn' t matter if the water is hot or cold. I could fill a 10 gallon bucket and pour it down the drain and would hear the knocking from the center of the house. I will hear the knocking in the sinks that are used more often. I will hear the knocking when the washing machine drains. I will hear the knocking when the two toilets used most often are flushed.

Is washer located in basement?
Do you have a sewage ejection pump?

Is washer located in basement?
Do you have a sewage ejection pump.

No, the washer is on the second floor next to the hot water heater. I do not know if I have a sewage ejection pump but I could look for it, I assume it would be in the basement at the main drain?

Yes, would be a pit in basement floor. Sewage would drain into it and then would be pumped back up to sewage line going out of the house to the street sewage line. If you stand next to it, you should hear the pump come on when a significient amount of water drains into it.

If your sewer pipe exits the house above the floor line and you have fixtures in the basement then you have a ejector pump. Regards, Tom

Could the sump pump be involved? Your thoughts? Tom

Yes, would be a pit in basement floor. Sewage would drain into it and then would be pumped back up to sewage line going out of the house to the street sewage line. If you stand next to it, you should hear the pump come on when a significient amount of water drains into it.

OK, I know I have a sump pump, but will look today and see if I have a sewage pump.

Could the sump pump be involved? Your thoughts? Tom

Meaning, making the noise? No, definitely not coming from the sump pump. Not sure if you meant something else though.

Just for your information. Sewage pump will look like sump pump but will have more pipes.

Just for your information. Sewage pump will look like sump pump but will have more pipes.

Yes, that does help, thank you!

One more time!
If your sewer pipe exits the house above the floor line and you have fixtures in the basement then you have a ejector pump. Don you have such a pump? Back to you, Tom

One more time! Don you have such a pump? Back to you, Tom

It do not believe I have one. I only have a sump pump, and believe my main sewer line is in the basement.

And is there water in the pit? Is this a operating sump pump? Let me know, Tom

And is there water in the pit? Is this a operating sump pump? Let me know, Tom

Yes, it is operating.

Could it be a "banging" that you hear? If so it could be the check valve c losing. Your thoughts? Tom

Could it be a "banging" that you hear? If so it could be the check valve c losing. Your thoughts? Tom

OK, if that is the case I would be able to hear the knocking standing next to the sump pump? I thought the sump pump was for ground water, not drain water from the plumbing pipes? Please advise and Thank you.

Sump pumps are ,indeed, for ground water. I'm just exploring possibilities. How about an PRV (pressure reducing valve, (see image) do you have one of those next to where the water enters your house? Let me know, Tom

Sump pumps are ,indeed, for ground water. I'm just exploring possibilities. How about an PRV (pressure reducing valve, (see image) do you have one of those next to where the water enters your house? Let me know, Tom

Yes I do

Next time you hear the knocking c heck out the PRV valve and let me know what you find . Tom

No knocking at PRV valve, no knocking coming from the basement area at all.

No knocking at PRV valve, no knocking coming from the basement area at all.
Then where's it coming from? Back to you, Tom

Then where's it coming from? Back to you, Tom

The sound is coming from the middle of the house (2nd of 3 floors).