What happens is that when I am finished with the spa and turn the jets
off at the spa and drain the water, the spa is finished with for the
night . Approx 15 - 20 minutes later one of the pumps sparks into life
again for no apparent reason.

The only way to stop it is to turn it off at the power, that is what I
meant by left on. Upon re reading my original post I understand the
confusion.