Hot tub won't heat up?

The click you hear is the thermostat turning the relay on and off, one thing you can try.....there should be an Access panel to heater unit and most units have a reset on located on them, set thermostat way low so if it only needs to be reset it wont try heating as soon as you reset it. most times it will trip again if trying to restart through reset on, reset then turn up thermostat......hopefully that's all it needs .good luck