i have a 2003 hot springs prodigy spa. it has run perfectly for about 2 years, since i bought it used. the problem with the jet pump started gradually, and now it happens all the time. when you turn on the jets the motor will cycle on and off as if it is trying to start then turns off then turns on then turns off etc. i have taken the pump and motor out of the spa and had it checked out at a local repair shop. it checked out fine. i have hooked the pump to 115v directly and it starts up and runs the jets normally. with the pump disconnected from the circuit board and my meter connected to the pump terminals i get 115v on the meter when i turn the jets on. i can hear the relays on the main circuit board click on and off when i press the jets button. with the pump hooked up to the terminals and my meter hooked up the voltage goes up to about 85v then 0v as the motor is surging on and off. the small recirculation pump and heater seem to be working fine as the water heats up to the set temperature and stays there. i have even tried isolating the pump relays one at a time to see if a relay could be the problem. first the hot side then the neutral, no luck the motor still surges on and off. i have also replaced the 20 amp circuit breaker in the panel suppling the 115v side of the spa. i hate to go out and start buying circuit boards without knowing what the problem is. since hot springs does not supply a service manual or circuit diagrams i do not know if some protective circuit is turning the motor on and off for some reason. has anyone seen this problem ? could use some help!

First I would make sure you have 12 gauge wire for that circuit. I've seen spas running on 14 gauge wire do the same thing. It can run fine for a while then start surging.
Other than that I think it might be a control box problem.
You could call tech support at Watkins to confirm.