Join Date: May 2016
Location: Deltona, Florida
Rheostats (potentiometers, dimmer switches, etc.) have a tendency to corrode at the connection. Sometimes, and temporarily, just spinning the "dials" back and forth a few times will clean the contact area. Then you can reset the proper position.
But if corrosion is the issue, this will only fix the problem temporarily.
If it's not too old a unit, I'd contact the manufacturer. My mother-n-law just got a brand new Pfister faucet because the 3 year old one developed a leak. A picture and an E-mail ... two weeks later, a faucet shows up on her door step.