"Bob" wrote in message ...
I own a duplex that has an upper unit and a lower unit. In the upper unit
there is often a problem with the temperature of the water in the
tub/shower. The water will be too hot and moving the hot/cold handle on the
tub/shower makes little difference(if you push the handle to the coldest
position the water will then become cold-but the correct adjustment in
temperature just doesn't happen). In other words when this is going on you
will have very hot water or you can adjust to very cold water but nothing in
between.

After about 5 to 7 minutes of this, you are able to control the water
temperature normally.

I would say this happens about 20% of the time you use the tub/shower.

I understand there are "mixing" valves to control this problem.

Where in the plumbing system would I install such a valve to solve the
upstairs tub/shower problem?

Is this a do it yourself project or better left to a plumber?

Roughly how much do these valves cost?

I believe the mixing valve replaces the shower valve you have. I wouldn't be surprised if your problem is a
malfunctioning "mixing valve". Try calling the manufacturer and tell them the problem. They may send you the needed
parts, as many of these have "lifetime" warrantees.

Bob