I have a shower stall with a single control knob that controls on\\off (pull out for cold and push in for off) and hot\\cold (left for hot, right for cold). The temperature setting on the gas-fired water heater is on the "normal" setting. Other faucets in the house seem to produce a lot hotter water when they run with only hot turned on. For a year or two now I've had to keep the combination hot\\cold on\\off handle almost all the way towards hot to keep the shower hot enough for a decent shower. I finally removed the round knob and the escutcheon plate to see what it looked like. There's a very small retangular cutout in the tile and the only thing that's visible are the two holes that mount the escutcheon plate. The diameter of the place where the knob mounts is a little bigger than the diameter of a nickel, and it appears to have what looks like the same type of fitting as with a garden hose valve when you remove the wheel handle - it looks simply an on\\off function - I didn't seen anything that looks like other mixing valves that I've seen in pictures - nothing that looks like any adjustment screws or the like.
Is this a situation where I simple remove and replace what the control knob attaches to? When I go looking for replacement parts, what's the proper terminology?
If it's going to involve removing tile and all that, I can learn to live with it.
Thanks!