I live in a house that was built by my parents in 1950. It's a pretty basic ranch. Two full bathrooms, both on the ground floor. The original shower control valves were both replaced by Symmons Temptrol pressure-balancing shower valves a number of years ago. Temperature at the water heater is set at 125 degrees. The two bathrooms are adjacent, fed off the same 1/2" copper line running from the water heater in the basement to the two tubs.
In one bathroom, the shower water can be cranked up as hot as I would want to stand under. In the other bathroom, the shower water is barely warm enough to stand under semi-comfortably, even with the shower valve wide open. Since my wife died five+ years ago that second shower hasn't been used except when a friend of my wife's visited from South America a year ago, and she commented that the shower didn't get very hot.
I took the valve apart and found that the piston was locked up by mineral deposits (I'm on a well with very hard water). I followed Symmons instructions, soaked it in white vinegar, and got it freed up. I have also adjusted the hot temperature limiter twice, to allow the valve to open farther in the HOT direction. Doesn't seem to help.
Any ideas?