I had 2000 hot springs Grandee model and just replaced the Heater with the Tri-Bend model. I also replaced the Thermistor and Hi-Limit Switch but the hot tub won't heat above 90 degree. I am assuming that the circulation pump is running because the air bubble is coming out from the bottom. The filters are all clean. I did touch and feel that there is flow coming out from the outlet line of the heater. I can't figure out why it won't heat above 90 degree. Please help!!