No service warranty?
Did the amp quit, controls, something else?
Is that volume control the slider or rotary type? I had a slider- type control puke and when that happened, the amp in the stereo receiver puked, too. If you have a multi-meter, check the resistance on each channel at the receiver end AND at the control- I also checked without the control or receiver connected because I wanted to know if the wires had shorted (they hadn't) but when I checked at the control, I found the problem.
What source(s) do you use for music at the pool? An AVR with app-based control would let you eliminate the volume control- I know those can be convenient, but I like to keep it simple and a volume control can add a point of failure, especially if it was installed in an outside wall and not in a closed junction box.