I'm actually having the same issue, after half an hour or more my temp begins dropping from 104 at a rate of about a degree every half hour or so and it's really annoying. I got my electrician to come over and he did an amp test on the power wire going out to the tub and with both pumps running and the heater on, i'm only drawing like 26 amps @ 230v. I am starting to wonder if the heater was set up for 110v or if my tub switches the heater off when both pumps are running. Anyone in here have any insight on this?