Possibly the "Sensors are out of Sync" (SnS or Sn) with Each Other.
With the the Pump ON, prior to Heater ON, the Sensors differ by more than 2°F (1.0°C), indicating one or both Sensors are several degrees off. The Sensors are Possibly Out of Sync with Each Other, or Not Indicating Close to the Same Temperature at Both Sensors. Monitoring the Sensors will Continue for 1 Hour. Test the Sensors, or Continue for a Detailed Test Procedure.
