There is crud in the lines before the valve. You can tear out the valves and
flush or use my handy "back flush" system.

1. Turn off power or gas to hot water heater.
2. Turn off cold water valve supplying cold water to the hot water heater.
3. Connect garden hose (going outside) to water heater drain and open drain.
4. Go to bathtub, place a cap or one of those shower on/off valves on the
shower. Turn center valve so water is directed to shower instead of tub.
5. Fully open cold and hot water valves for shower.
6. Let flow for about 10 minutes.
7. Do same with faucets, except you can't easily cap them, so hold rag over
faucet.

What you are doing is getting the cold water to flow in one end of the
faucet then flow back out the hot water side. And hopefully this will also
move the crud back to the hot water heater, and out the drain. i.e. back
flushing the hot water pipes.

"Mike" wrote in message
I had a new water heater installed about a year ago. I have noticed
that over the course of the year the pressure has gotten worse to the
point that in the bathroom furthest from the hot water heater there is
barely any pressure coming from hot water in bathtub. When they
installed the new water heater they added a valve on the inlet side of
the water heater. Is it possible that this valve is either corroded
with sediment or bad all together. Please any help would be appreciated.