Hello. I have a raised hot tub that spills over into my pool. My Mastertemp 400 runs normal if I have the valves positioned for the pool but shuts off after a few minutes when I have them positioned to isolate the hot tub. I have a pentair variable speed pump, which I run up 3100 for the hot tub (2700 for the pool). When the heater kicks off I get a service light but no error code. I surfed the internet. It said maybe it is water flow issues, so I cleaned my cartridge filters again. No change. I replaced the circuit board and touchpad (with an Amazon $85 one). No change. Except for the heater kicking off the water appears to be circulating well in the hot tub. Any suggestions?