Check sensor wires for cracks or damage that may indicate the presence of a rodent.
- Inspect the connections of both sensors on the circuit board. The plugs must be clean.
- If the sensors are not totally failing but are showing excessive (1.0°C/2.0°F or more) difference between the two sensors when not heating (a possible cause of Sn/SnS/SENSOR SYNC, HL/HFL/HTR FLOW LOW, and LF/ LOW/FLOW/messages), do the following: Note which sensor is reading consistently higher (A vs B or t vs H).
- Unplug the two sensors from the circuit board and exchange their positions (i.e., plug the one that was in the “Sen. A” jack into the “Sen. B” jack and vice versa).
- Press a panel button if any “stray” faults appeared during the process. (Stray faults are normal when sensors are unplugged then plugged back in while the system is running.)
- Within a minute or so*, see if the same or other sensor is now reading consistently higher: If the same sensor (A vs B or T vs H) is reading higher after the sensor interchange, the problem is on the circuit board. Replace the circuit board.
If the opposite sensor is now reading higher the problem is with the sensor(s). Replace the sensor set.
*If you wait more then 2 minutes after plugging the sensors back in, heating may start (even outside a filter in Economy or Sleep mode) due to a stray Cd/CLd/COLD WATER condition usually detected when sensors are being plugged in while the system is running.
If there is a message indicating an open or faulty sensor: Unplug the sensor set (leave the original sensors) in the heater and plug in the test sensor set. Put both sensors into the same cup of warm water (ideally above the set temperature, so the spa won’t try to heat during this test, as there is no heater protection during this test) and verify that they read the same temperature (within 0.5°C/ 1°F).
If the problem is not resolved replace the original sensor set.