When you drain your spa make sure to always refill it by placing a hose in the filter box., otherwise you can get an air lock in the plumbing system. There will be no water in the heater and you will get an error message on the touch pad. You can try pushing the filtration pump button or pump 1 for spas with 2 speed pumps on and off to try and get the water flowing. If this doesn’t work you’ll have to remove the cabinet panel underneath the touch pad and unscrew one of the barrel unions on the pump. You will hear the air escaping and see the water start to leak from the union. Retighten it and try the pump again. Now it should work.