On Sun, 19 Feb 2012 20:18:08 +0000 (UTC), DerbyDad03
wrote:


Wouldn't the restriction be there at all times, always restricting the
flow?

There's pressure, and flow (volume.)
When the faucet is off, all water in the piping gets pressurized.
But once the pressure has reduced by ejecting water from the faucet,
it takes sufficient flow to maintain the pressure

The timing doesn't seem right for that from what you said - 20
seconds?
But if you have an expansion tank, it may take that long to
depressurize. Then the flow restriction shows itself.
Since you have copper, a valve is the most likely suspect.
Another WAG is the HW tank is scaled up enough to restrict flow.
If you've pulled all the associated valve stems and verified the
valves are unrestricted, the only thing left is to take apart the
lines before and after the tank to pin it down.
I think you'll live with it as it is, but maybe I'm wrong.

--Vic