Last night when trying to give the kids a bath only hot water would come out of the fauscet for the tub and shower. I tried the adjecent fauscets for the sinks and they worked fine. The only adjustment I have made in the last several months was turning down the temp on the water heater, but I would not think that would have any affect on cold water. My guess is I either have a broken value for the cold water in the shower water control unit or there is a clog in a cold water pipe somewhere. Anyone have any ideas on how to trouble shoot this one?

Image of a similar unit: