Pipes knock when tolet flushes


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Old 01-31-09, 11:07 AM
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Cool Pipes knock when tolet flushes

When ever the tolet flushes there is a loud knock of the pipes in the basement as soon as the tolet stops filling. If I turn on the bathroom sink prior to the filling the knock does not occur but as a soon as the fill completes there is a rush of air at the sink. Also when the knock occurs there is a sight discharge of water from the pressure relief valve connencted to the tankless hot water heater. The home has a boiler which is less than 2 years old and there is no air in the system. The bathroom on the second floor does not have this problem. I have changed out the fill tube with no success. Everbody I have talked to is puzzled. Any help is appreciated.
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Old 01-31-09, 01:27 PM
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Banging Pipes

rferenc: If you are getting banging pipes and water comming out of the relief valve its a good chance yoour water pressure is too high, get a pressure gage and check the incomming pressure, it should run approx. 60lbs, 80lbs is usually code max.

If it is more than 80lbs you will need a pressure reducing valve, luck
 
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Old 02-01-09, 04:08 AM
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Another thing to look at is, what kind of hot water do you have? If it has a tank type and you are on city water, you may need a thermal expansion tan installed or replaced. Without this tank in certain situations will cause a high, sometimes extremely high water pressures in your water piping. This high pressure can cause the relief valve to drip or blow off if pressure gets too high.

I would take a pressure reading of your water system and possibly need to install a pressure reducing valve as stated earlier. You may also wish to add some watter hammer arresters in the system.
 
 

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