Have a two handled faucet in a clawfoot tub. Pressure is fine for both hot and cold, however when the shower is running the cold water knob slowly moves toward the closed position. In otherwords, the handle actually moves on its own. You have to continually open it back up in order to keep your desired temperature. I assume that this caused by pressure somewhere. Any ideas on how to remedy.

What's your house pressure?

The pressure seems fine. Perhaps the cold water pressure is being overmatched by the hot. Its actually tenant occupied and I haven't actually seen the problem yet. Maybe I should check the cold water line and make sure the pressure is OK. Asssuming it is, any idea what could be causing this.

I'm going to put up a image of a washer type tub faucet with a diverter. Yours hasn't a diverter but otherwise they're the same. To prevent the cold water stem from creeping snug up the bonnet packing nut,(the top nut). Let me know. Regards,Tom