DIAGNOSIS: The set screws inside the knobs have loosened or fallen out. Each knob is held onto the control shaft by a single small set screw.
FIX:
- Pull the wobbly knob straight off the control shaft.
- Look inside the knob's hollow stem. You'll see a small hole for a set screw (often a hex/Allen type, sometimes Phillips).
- If the screw is still in there, simply tighten it firmly with the appropriate tool while the knob is off.
- If the screw is missing, you need a replacement. It's a standard metric set screw (often M4 size). Hardware stores have them.
- Insert and tighten the screw, then push the knob back onto the shaft, aligning it with the "Off" position.
IF THAT DIDN'T WORK: If the knob is still loose after tightening, the control shaft itself might be worn or broken. This would require replacing the entire infinite switch behind the panel.
HEADS UP: Don't overtighten the set screw or you risk stripping the plastic threads inside the knob. Snug is enough. Also, make sure the knob is aligned correctly when you put it back on, so the off position is accurate.