I recently purchased a home that was built in the 1950s. The house is
supplied with city water, has a gas water heater, and most of the
supply lines have been converted to CPVC.

Within the past week, the shower valve was putting out "very little"
hot water. The shower is equipped with a single handle American
Standard faucet/valve. I removed the handle and checked the anti-scald
setting to ensure that it was set on the hottest possible setting.
Next, I checked all the other faucets in the house to ensure they were
getting hot water, which they all were. Finally, I checked the shut-
off valve on the shower hot water supply line to ensure that it was
completely open, which it was. At this point I was stumped, so I
called a plumber.

The plumber came to the house and performed all the same checks that I
did. He then informed me that the supply risers going from the
basement to the 2nd floor shower were galvanized pipes and could have
corroded, causing water deposits to clog in the valve or somewhere
else in the pipe. To remedy this, he tried to flush out the pipe by
turning the hot water shut-off off and on. Some debris did come out of
the pipe. After that, he put everything back together and still no hot
water from the faucet. He then made the determination that since the
risers were galvanized and the rest of the supply lines were CPVC, the
water pressure entering the shower valve must not be correct.
Apparently, plumbing code requires that shower valves be equipped with
a pressure balancing mechanism, and if the pressure is too low/high
then hot water will not come out of the faucet. To completely fix the
problem, he said that the galvanized risers would have to be removed
and be replaced with CPVC risers.

Does everyone agree that the only way to completely fix the problem is
to replace the galvanized risers? For the time being, we turned the
cold water shut-off valve to about 3/4, but this causes the water to
be fairly hot, even when the valve is turned all the way on cold.

Please help!