I have a 2 handle shower/bath faucet with spigot diverter to run the shower. A few times in the past 2 weeks, but not every time, when I turn off the hot handle, the hot water just keeps running. Oddly, if I turn it back on all the way, then turn it off again, it always shuts off. This isn't a pressure issue, but certainly suggests something is wrong. No reason to wait for total failure. Any ideas? Thank you!

 

You need to replace the cartridge, if it is in fact that type of valve. Tell us the brand. Send a pic if possible.

 

Here's a shot of the valves; I didn't see any brand names but I do have an access panel behind the wall. Perhaps it is imprinted on the brass manifold? Is it possible the handle itself is slipping against the cartridge?

 

There are two basic types that your faucet could be depending on it's age. One would require replacing the valve cartridge and the other you just need to replace a washer. In either case it's a pretty quick and simple job if you can get the knob off (sometimes the screw in the center of the knob corrodes in place and can be very difficult to remove).

Turn off the water to your house. Open/turn on the faucet until water stops flowing. Close the tub drain or put a rag over it in case you drop a screw. Remove the screw in the center of the knob then pull off the plastic knob. Then underneath you'll see the flats where you can use a wrench to remove the valve body. Once that's out you'll know what type you have. Most home centers and plumbing suppliers carry everything you'll need.