knocking sound only when water is off

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awalts said:
Nope, I have a normal gas heating system, not a hydronic one. The pipes are just cold water lines coming off the main and heading to the outside spigots. The tags were put on by the house inspector just marking what each valve does (front, back, water heater etc). I'll turn off the toilet (s) this weekend - I wanted to do it when I was home for a decent amount of time.
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We're does the shut off that is on the off position go?.. And why is it off?....

You have or don't have your heat on
Is it controlled at the radiator or thermostats.
 
I turned off the water to each toilet (and then all of them at the same time), and the knocking still persists.

The two valves (one shut off, one not) go to the outside spigots (front and back). The knocking sound occurs regardless of their on/off setting.

Lastly, another video of the knocking. Sorry for the initial camera movement. The knocking comes on very suddenly at the 19 second mark, grows in intensity and volume, and then stops after about 4 seconds. It starts and stops in spurts like this, sometimes once or twice, sometimes many times over a 30 minute period.
[ame=http://www.youtube.com/watch?v=U3TY_Md2zes&feature=related]00002.MTS - YouTube[/ame]

If it is the pressure reducing valve, any thoughts on how much that costs to replace?
 
I have an update to add to this knocking issue ...

I bought a pressure meter and attached it one of the outdoor spigots. Normally the water pressure is about 70 psi and the needle does not move. However, when the knocking sound occurs, the needle shakes/fluctuates between 60 and 70 psi. So long as the noise is being made, the needle shakes. As soon as the knocking stops, the needles returns to holding steady at 70psi.

Any thought now on what needs to be fixed?
Thanks again
Avram
 
Any chance there's a recirulating pump on the hot water line? It cirulates the water so as soon as a taps turned on the waters hot.
 
awalts said:
I have an update to add to this knocking issue ...

I bought a pressure meter and attached it one of the outdoor spigots. Normally the water pressure is about 70 psi and the needle does not move. However, when the knocking sound occurs, the needle shakes/fluctuates between 60 and 70 psi. So long as the noise is being made, the needle shakes. As soon as the knocking stops, the needles returns to holding steady at 70psi.

Any thought now on what needs to be fixed?
Thanks again
Avram
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I am not a plumber, but I have had two different Gas regulator, one LP and one Nat gas, that were a little to much clearance in side so when they would operate at times they would not only go up and down, they would violently vibrate and raddled all the gas piping in the house. Have you had them change the regulator yet. When that happened to me the first time i could not believe the noise it made. I had just put the new boiler system in so the regulator was new but defective. Paul
 
So when exactly does the sound accrue?
Did we eliminate heat? Because it happens when the heat is off?
Is anything running dishwasher shower ect? How do we know that it's hot water line we don't so how about fluid master goes bad happend to me a few times it made the hole line shake like crazy I thought it was a ball valve not opened all the way but no it was fluid master.
Turning on the out side spickit could cause this as if you have alot of pressor in your lines check your boiler and or hot water heater check for feeder valves to either boiler or tank to give it water.
If any circulators u have feel them make shore they are not over heating.
 
70 PSI is a whole lot more then I've ever seen a fresh water system set it. The highest I've seen is 50 PSI, and I've worked on and built hundreds of homes in my life time.
 
70 PSI is a whole lot more then I've ever seen a fresh water system set it. The highest I've seen is 50 PSI, and I've worked on and built hundreds of homes in my life time.
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The only time I had city (county) water in my entire life was ten years ago and that static pressure was 85 psi.
 
Have you been lucky enough to be able to time it so you can actually touch the various pipes while the knocking is going on to see if it's a particular line?
 
Any luck in finding what the real problem was?...we are facing the same issue in our house....please help
 
It turned out to be the Water Pressure Reducing Valve. I lowered the household water pressure (loosened the valve) and then slowly brought it back to the original pressure. And the knocking went away. I can't explain why it worked, but it did. We haven't heard the knocking sound in over a year.
 
awalts said:
It turned out to be the Water Pressure Reducing Valve. I lowered the household water pressure (loosened the valve) and then slowly brought it back to the original pressure. And the knocking went away. I can't explain why it worked, but it did. We haven't heard the knocking sound in over a year.
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Something may reinitiate it, but at least you know a fix that works for now.
 
hi, we have exactly the same problem as yours. Where did you find your water pressure reducing valve? does every house has it?
 
jj_iitk said:
hi, we have exactly the same problem as yours. Where did you find your water pressure reducing valve? does every house has it?
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Not every house has one but every house should (if connected to a municipal source). They're typically located right after the main shutoff valve where the water enters your house.

watts_prv.jpg
 
jj_iitk said:
does every house has it?
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You want more than 20 PSI static pressure into your house for sanitary reasons and less than 80 PSI to make the pipes last long.
Max flow rate may be 16 GPM but there may be a minimum for sanitary reasons.
 
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