I have an older Jacuzzi Caressa model 8780000. the problem is that when the temp drops low enough to kick on the thermostat, the pump comes on low (as normal) but the heater does not. If I cycle the power button to Jets, the heater comes on. I can then push the button again for htr/filter and the heater will stay on untill the tub comes back up in temp. but after it cools down again I have the same problem. Can it be the flow switch? Help it's November in Pittsburgh!

It does sound like a flow switch problem. Check to see if you have a knurled knob at the top of that switch, and turn it one turn counter clockwise and see if that fixes your problem. It may have a drop of glue on it to keep it from turning from the factory. Just break that loose.