Report "We have a Pentair Mastertemp heater. It comes on, fires up and starts to heat. After less than 10 minutes it shuts off and the red Service Heater light comes on. Sometimes after several attempts it will stay on long enough to heat the pool a few degrees or even heat the Spa to full temp but most times it just shuts off. The exhaust pipe is blowing out really hot air and has singed the side of house. Tech came and saw flue stack sensor light was on and replaced flue stack sensor on advice of factory tech he spoke to by phone. But the problem is still happening and light is on despite new sensor. What should we do"