Why is my shower valve's temperature control erratic?

drywall_dan

We bought the house recently. House built in 1985; shower age unknown. Has one of those valves where in/out controls flow and rotation controls temperature. With the handle pointing ten o’clock, once the pipes warm up, it is too hot to use. Turning it gradually makes little difference, until it gets to two o’clock. At that point, the flow suddenly increases and it becomes cool. Turn it back to ten o’clock and the temperature is ”just right.” We...

Originally asked by WGroleau on Stack Exchange (diy) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

Could be a misbehaving "anti-scald valve" in the shower control, if it has one of those. Figuring out what valve it is and replacing the cartridge and any other serviceable wear/age parts ( i.e. if it has anti-scald valves and the function is not built into the main cartridge, but is servicable by replacing other parts) would be a logical first step to addressing the issue. If the valve does not have anti-scald technology built in, it may just be a bad/worn valve cartridge Wholesale valve replacement would be much more work (but would ensure up-to-date anti-scald valve technology.) However, a temperature-control valve on the hot water line to limit the temperature of the hot water flowing...

Full answer by Ecnerwal: https://diy.stackexchange.com/a/332174 (CC BY-SA 4.0).

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