I have an 2000 Marquis Reward RS series spa. The pump that is used for Constant Clean filter cycle (Zone 1B jets) just recently started coming on at high speed only.

When on filter cycle or during normal usage, this pump only works at high speed. I am afraid this pump is going to be overworked since it normally will shut off after 15 minutes at speed.

Am I looking at a pump problem or control problem? Any help is appreciated.

Check your voltage at the motor, there should be a wiring diagram on the motor, make sure you are getting voltage switching between High and Low at the terminals. The control could be bad and not switching back and forth.