Spa is several years ols but pack is about 3 or 4. It is a Balboa pack. Had been shut down for several months, cleaned it out filled it up and it did come on and heat but the next day it was off and the controller had FL instead of a temp. Please tell me what's up. Thanks

Check your filter, if it is clean then you could have a bad pressure switch. A bad pressure switch would give you the FL on the top side.