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cowabunga1000 wrote at 2016-05-02 05:13:56
The pipes in my house have been making an intermittent tapping noise for years and I've never been able to figure it out.  When it happened, it was a very regular knock in the pipes, almost like a metronome.  It would start up, knock about once a second for a few minutes and then stop.  Turning off the main valve to the house stopped it, but it would start up again when turning the water back on.  I have a pressure regulator in the main line, so I called Watts, the manufacturer, to see if they could help.  Shazam!  After a couple of minutes of chat, the tech explained that the regulators have a backflush valve in them that opens if the pressure inside the house exceeds the incoming pressure.  That can happen if the incoming pressure is about equal to the pressure setting on the valve and the water heater kicks on.  Heating the water makes it expand, and if no water is running that excess pressure has to go somewhere. If heating causes the internal pressure to exceed incoming, that backflush valve will start operating - and it makes a very regular "thunk" sound that can be felt and heard in the pipes.

So...the answer may be that you need a thermal expansion tank - basically, an air chamber connected to the cold water supply line to the water heater that absorbs the pressure difference when hot water expands and helps keep the pressure in the system from suffering spikes.  It also keeps the back flow setup under tapping sounds!  Easy to add a tank for less than $100.  

cowabunga1000 wrote at 2016-05-23 05:35:46
If the supply pressure to your house and the internal pressure (past the pressure regulator valve) are about equal, the inside pressure can go higher when the hot water heater kicks on.  If the pressure inside exceeds the supply pressure, there is a backflow valve in the regulator that opens momentarily to equalize inside and outside.  It will cycle until the hot water heater shuts off.  My plumbing was making a very regular click-goosh sound, almost like a metronome.  Didn't seem to hurt anything, just an odd sound.

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Leo Luczak


I am a Certified Building Official, and I am certified by the International Conference of of Building Officials as a plans examiner and as a commercial and residential building and plumbing inspector.


I have been the Building Official for a small town in Alaska for the last 14 years. I also spent 20 years working in construction. I don't know that much about wells and septic systems.

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