In Reply to: Re: Plumbing Puzzle posted by Jack - Iowa on June 10, 2018 at 14:27:49:
If the shower valve is 28 years old it is probably not the balancing valve type so it should not change the water temp while water is set and running. If it is a gas heater then you have a thermocouple that is possibly going bad. You may have a temp balancing valve down at the water heater where the hot water comes out of the heater. That could be going bad or just need a good cleaning. Some you can take apart.
The big question now is will it do that again..?