Ok so I realize that the lukewarm shower but hot water everywhere else is a huge topic, but trust me I've researched this to death and have done all the normal responses. The shower was originally hot, and started to only put out lukewarm water about mid september.
I've got a Symmons TA-10 shower valve, When turned all the way up, the water is only lukewarm and pressure is reduced by about a third. Hot water is scalding in the bathroom sink and kitchen sink, as well as the washer. The only other symptom is reduced pressure in the kitchen sink when turned all the way toward hot.
Things I've tried so far.
Adjusted the hot water screw on TA-10 to allow more hot water (No change)
Removed TA-10, checked the function (that thing makes the noise), cleaned it, soaked it in vinegar, replaced corroded O-rings, (no change)
Completely replaced the TA-10 with two brand new components, adjusted the hot water out put, No change
A little back story on the house, I on the first floor of a 3 story house in Boston. The house is old but it was recently renovated with new appliances. We have a RUUD gas water heater, located in the basement directly below the kitchen. There is about 25 feet of piping between the water heater and shower.
Thanks in advance!
First thing I would try is pulling the cartridge/spool out of the valve and turn the water back on to check temperature and pressure with it blowing out the valve body unrestricted.