When toilet is filling up hot water comes out of the shut offed faucet in another bathroom causing Water hammer. IS the water pressure to high? is the value broken on the hot water side? faucet does not leak when shut off.

uncle buck, you said water was coming out of a faucet that was turned off? as in it aint on?

unc, if you think your pressure is high, then buy a gauge at the plumbing supply, that fits on your outside hose faucet
the gauge should be a 100 lb gauge
and normal city pressure is 45 to 55 psi
if over 55psi you may need a pressure reducing valve
if its just 60, dont sweat it, but 65 and up..

yes the faucet is turned off and water is forced out of the turned off faucet when toilet is flushed. when I turn on and off the faucet the hammering sound stops even though the toilet is still filling. I have turned down the flow of water at the main but it still happens. I know we have high pressure when I filled our 25000 gallon pool in 20 hours with 2 hoses. one a 3/4 and the ohter 1/2 inch.

Trying to "turn down" the pressure by closing the main valve some will do nothing but reduce the flow. Once the flow stops the pressure with be right back where it started.

2 reasons for water hammer
loose pipes, or pipes straped to tight
i know thats a non answer, but its the truth
90% of the time its loose piping, try and find the pipe and cut hole in wall and strap it
as far as your pressure
buy a gauge from the plumbing supply house
that will install on your outdoor hose faucet
gauge needs to be 0-100 lb test gauge, tell the guys at supply house what you want, they will give it to you
if pressure is around 50 psi, thats ok. if its above 70 psi
you will need to have a pressure reducung valve installed on the main line coming into the house
try turning down the valve at the fixture.. mite work
your ho- do- voodoo faucet that comes on when water is off
yank that evil sob out and replace. i hate evil acting fixtures frodo

Was that a Labyrinth refference? Ho Do you do voodoo?

Thanks for the reply too.

whats a labyrith? no i dont do voodoo. i just get crazy on these keys. i have seen all kinds of crazy stuff at peoples houses
i should write a book. i call fixtures that do crazy things, that have no reason to do it. haunted or possessed
its a term that "just" fits.. like a toilet that flushes at 12 am
with no one in the bathroom, or a wwet spot in the middle of a bathroom floor and NO fixtures are leaking. etc...