DO NOT DRAIN IT!!!! That is the worst thing you can do. The best thing you can do is get a small space heater that has some sort of thermostat on it, even if it is just low, medium, and high. Put that in the equipment area on medium and close everything up and cover the front with a blanket or tarp. That will keep your spa from freezing for as much time as it takes for the repair guy to get out, especially if you leave the spa on so the main pumps can fire up every now and then.