Hello. My 2000 Jetsetter heats up the water fine when plugged in but when the water cools down the heater does not kick back in and heat it up. The Ready light stays on though indicating it has reached the desired temp. If I unplug the spa then plug it back it in it resets and heats the water just fine but will eventually cool down again. I tested the thermistors thinking the temp control one might be bad but it reads 5.6k ohms, right on spec. The Hi Limit sensor reads 11k ohms, way out of spec but I don't see how that could cause this issue. When that one goes bad the water gets too hot and lights start blinking. Any ideas? Thanks.