How does a thermostatic valve typically break and be repaired?
I'm considering using thermostatic/volume/diverter valves in my bathroom. In my second bath, I have a Moen pressure balancing valve. In 20+ years, the only problem with it was a slow leak one time which I simply fixed by replacing the cartridge.
How do thermostatic valves break or wear out? What are the symptoms - only cold water, only hot water, or? How are they repaired - replace a cartridge or the entire valve body?
As reference, I will use a major brand (Delta, Moen, Grohe, Kohler). Am leaning towards Kohler.