Have a two story house with kitchen, main bath, guest toilet and laundry room on first floor, and two bedrooms upstairs with one full bath each. The water heater is a 55 gal gas operated, located in the crawl space. There is an expansion/pressurized tank on the hot water line of the house as well.
Yesterday, out of the blue and without any warning, the shower in the main bath went from hot to lukewarm then cold after about 30/45 seconds of running. The sink in the same bath would put out scalding hot water, as did the kitchen sink and any other outlet in the 1st floor. Turning the mixer valve control to max hot puts out warmer water, just enough for one to shower.
Checked upstairs and one of the bathroom showers displays the same symptom, while the other one works fine. Again, all faucets in the 2nd floor put out hot water as expected.
I checked the anti-scald on both shower mix valves and these don't seem to have them (Price-Pfisters - MFD 2007), but after that I'm out of options. Today both showers continue to do the same, while the third one upstairs (the one least used) works fine.
Where should I start looking? Is it possible that both mixer valves would have gone bad at the same time? What else could be causing this?