Test your water pressure past the pressure reducing valve.
Where is my water pressure regulator.
They can eventually plug with debris.
This will cause your water pressure to be much lower when a second or third tap is.
Inside a water pressure regulator has a variable spring loaded diaphragm that automatically widens and narrows depending on the amount of water pressure entering the valve.
If it exceeds 50 p s i.
It usually has an adjustment screw on top.
Your pressure relief valve let s stop using acronyms is probably located on your water heater it is actually a temperature pressure relief valve.
Sometimes a pressure only relief valve will be located on supply piping also.
Be sure to leave one faucet open enough to get a current reading of the pressure after the pr valve.
Try to adjust the pressure on the valve.