shower water temperature fluctuation problem

hello, i'm having a problem with my water temperature when I shower. Whenever I turn the shower on, even at a low pressure, the water temperature will go from from hot to cold to hot without reason. it seems to be related to the water pressure b/c when it gets colder, the water pressure increases slightly even though I'm not turning the controls. the fluctuation gets worse if I turn the water on all the way so I can't use the shower at full blast.

Any ideas what needs to be done?

Thanks in advance for the help!

Can you post a picture of the shower valve?
New valves come pressure balanced. If you have old piping and the old non-balanced valve, then adding an expansion tank helps with pressure swings.
If you have a pressure balanced valve and the temperature is changing, then you may need some work with the cartridge.

Thanks so much for the reply Terry. It's the 11th floor of a building built in 1983. Any idea what the work would entail, how long etc, and about how much it would cost? Thanks in advance


I attached some pictures but not sure they came out so here are links:
http://www.flickr.com/photos/29161142@N02/7507699940/in/photostream
http://www.flickr.com/photos/29161142@N02/7507700236/in/photostream
http://www.flickr.com/photos/29161142@N02/7507699590/in/photostream

Thanks again

i have old valves so I'm thinking I should have pressure balanced valves installed. Would you know if that require putting a hole through the wall and what that process entails? Thanks again

Moen has a remodel plate for their Posi-Temp tub/shower valve. You cut the tile from the supplied template and that gives enough space for a plumber to get in there and change it.