I have had this knocking pipe problem for a couple of months, please help.

I have read a lot about the water hammer phenomenon since this pipe noise problem started bothering us. Unlike most of the stories I read, our problem doesn't seem to be associated with any specific faucet. It typically happens in the night when nobody is using water in our house. It sounds like the pressure is building up and gets real loud after a while. If I open a faucet (any faucet) and let the water run for a moment, the noise would go away. Kind of feel like the air (if it was air) was released by turning on a faucet. But later it will come back again.

I had thought this might be related to a false pressure reduction valve thus the water pressure was too high in our house. But I tried to adjust the valve (turning the screw counter clockwise) and it did decrease the water pressure (water runs at a much lower volume). So I think the valve works fine. I also tried to shut off the main water valve and drained all water for the house as other people suggested. Didn't work either.

Now I am running out of options. Could anybody help me please? Thanks.

Not water hammer. Water hammer is a big bang when a valve is turned off quickly. What you describe sounds more like a leaking toilet with a loose washer. Try turn off the stop valves at the toilets and let us know if the noise continues. How long is the duration of the noise.

Harold's bang on! This sounds like a toilet problem.

Let's reverse the washer first. Shut the water off under the tank and take the lid off. Remove the three screws on top of the ballcock,(sae image) and pull the stem,washer and float assembly up. Pry the washer out and turn it over. Seat it back firmly and see if that doesn't help. Before you reassemble hold your hand over the ballcock and turn the water back on to flush out the supply.
Sometimes the problem is caused by the ballcock trying to fill while water is seeping out of the tank. The sound you hear is the washer vibrating against the seat of the ballcock. First check there linkage between the flapper and the flush lever. It should have 1/4" of play when your tank is filled. The water level should be 1/2" below the white overflow tube after the tank's filled. Next feel the flat side of your flapper. Does it have wavey edges? Do your hands come away black? Replace it if it does. And last check the seat itself. Any nicks or rough spots? If so click on back. There are replacement seats that glue right over the old one and are easy to replace. One of the above should take care of your howling.

This happened in a new house some years ago. Only at night and in the early morning. They thought the house was haunted and were about to move out. I caught it in the powder room toilet. It would vibrate and the pipes in the wall would pick it up and carry it all over the house.
. Hope this helps you out and thank you ratting my answer. TOM

Thanks for your answer. I thought the toilets were the culprits first too. So I did watch the meter to make sure there wasn't any leakage (maybe too minor to affect the meter reading?) I'll shut off the water to each toilet and check again.

Usually the sound starts like water flowing through the pipe loudly and eventually the pipe starts rattling. The whole process lasts about a minute or so. Usually this is when nobody was flushing the toilet.


Not water hammer. Water hammer is a big bang when a valve is turned off quickly. What you describe sounds more like a leaking toilet with a loose washer. Try turn off the stop valves at the toilets and let us know if the noise continues. How long is the duration of the noise.

Thanks a lot. I will check the toilets immediately.

By the way, now I feel much better as at least I haven't thought my house is being haunted or anything so far. :D


Harold's bang on!! This sounds like a toilet problem.

Let's reverse the washer first. Shut the water off under the tank and take the lid off. Remove the three screws on top of the ballcock,(sae image) and pull the stem,washer and float assembly up. Pry the washer out and turn it over. Seat it back firmly and see if that doesn't help. Before you reassemble hold your hand over the ballcock and turn the water back on to flush out the supply.
Sometimes the problem is caused by the ballcock trying to fill while water is seeping out of the tank. The sound you hear is the washer vibrating against the seat of the ballcock. First check ther linkage between the flapper and the flush lever. It should have 1/4" of play when your tank is filled. The water level should be 1/2" below the white overflow tube after the tank's filled. Next feel the flat side of your flapper. Does it have wavey edges? Do your hands come away black? Replace it if it does. And last check the seat itself. Any nicks or rough spots? If so click on back. There are replacement seats that glue right over the old one and are easy to replace. One of the above should take care of your howling.

This happened in a new house some years ago. Only at night and in the early morning. They thought the house was haunted and were about to move out. I caught it in the powder room toilet. It would vibrate and the pipes in the wall would pick it up and carry it all over the house.
. Hope this helps you out and thank you ratting my answer. TOM

I turned off the water to all toilets in my house. But the noise still continues in the night. Unless I open a faucet and let the water run for a moment, the noise won't go away. So eventually I had to turn off the water to my entire house from the main valve. When I open a faucet, I can tell that there's lots of air in the waterline.

Pulling my hair now.:confused:


Not water hammer. Water hammer is a big bang when a valve is turned off quickly. What you describe sounds more like a leaking toilet with a loose washer. Try turn off the stop valves at the toilets and let us know if the noise continues. How long is the duration of the noise.

Are you on a pump or city water?

City water


Are you on a pump or city water?

When I open a faucet, I can tell that there's lots of air in the waterline
Tell me more about the air in your lines. Has the city been doing any work on the main? Call the Building Department and ask and then let me know. Tom

Turn off ice maker in fridge tonight. Do you have any lawn sprinklers on timers. How long has this been going on?

Since this started happening, I had turned off the valve to the water hoses outside my house (it's a townhouse and has no sprinklers). My fridge doesn't have an ice maker. Should I also turn off the water to the wash machine?


Turn off ice maker in fridge tonight. Do you have any lawn sprinklers on timers. How long has this been going on?

I don't know how the air gets in there. I think it has some to do with the pressure? Even if there had been some air in the system, I already tried to drain out all the water. Another clue is, the noise started after we came back from a one week vacation. Before we left for vacation I turned the water heater's temperature setting to vacation. I don't know if that has some to do with this problem.

I didn't notice any water related work in my neighborhood.


Tell me more about the air in your lines. Has the city been doing any work on the main? Call the Building Department and ask and then let me know. Tom

Is there a PRV, pressure reducing valve, next to where the water enters your house? Let me know. Tom

Yes. This had been the original culprit I thought of. Initially I adjusted the screw to see if the water pressure actually decreases and it did. So I thought that meant the PRV was OK (wrong conclusion here). Last night I bought a pressure gauge back and found out the pressure was over 100psi and would not drop even when I turned the screw all the way out (the upstairs shower still lost water volume ). So this morning I bought a new PRV and replaced the old one. Now the noise is gone. I think the problem has been resolved.

Thank you very much for your inputs.


Is there a PRV, pressure reducing valve, next to where the water enters your house? Let me know. Tom

Thank you for the update. I(f we can ever help in the future just ask. Regards. Tom