Diagnosis
The control knob's internal connection to the potentiometer (variable resistor) is loose or the knob itself is cracked.
How to Fix It
Unplug the unit. Firmly pull the timer knob straight off the shaft. Inspect the knob's plastic insert for cracks or a worn shape. If the knob is good, push it back onto the shaft until it seats fully. It should have slight resistance when turning.
If That Didn't Work
If the knob is cracked, order a replacement from PowerXL. If the knob is fine but the shaft underneath feels loose or wobbly, the control board's potentiometer is failing. This requires board replacement.
Heads Up
Do not use tools to pry the knob off. You can damage the shaft. If the timer is erratic, it's a sign the control board is failing and may cause inaccurate cooking times or temperatures.