I have a hot tub with a balboa system 2000 controller/heater unit. After a very cold winter, and one during which the kids left the cover off all night during below freezing weather, the heater will not get above 80, however it does seem to maintain that temperature. Is this a thermostat problem? Pump works fine and water pressure seems ok. We drained out the water to clean and refill, but should we take out the balboa and have it checked? it's expensive to replace at approx $500 but I don't know if spa dealers can check out the system without coming out and charging me an arm and a leg.

Sounds more like you've got a heater element problem, which isn't a $500 solution. Most Balboa Instruments™ systems are very durable and shouldn't need to be replaced completely.

The 80 degree thing you're seeing is the effect of the pump motor heating the water (which isn't much), and not the spa pack.

Do you see any kind of indicator on your spa side control to indicate that it's heating?
Do you have any error messages on your display?
Does your spa run 24/7 trying to heat the water?
Do you have the ability to measure the voltage at the heater element?
Is this a 115 volt installation or a 230?