- Check sensor wires for cracks or damage.
- 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 (2° F / 1.0 °C 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 interchange them (ie, plug the one that was in the A or t jack into the B or H 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 about a minute, 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 than 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 (but leave the orignal 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 1°F/0.5°C).
- If the problem is solved, replace the sensor set. If the problem is not solved, do not replace the sensor set.
- Plug in the original sensor set to verify that there is not a connection problem.
- If the problem continues after following the above steps, then replace the circuit board.
- If you cannot get readings of the sensors on the topside panel even in M7 Test Mode / Analysis Display Mode (for example, because the system always indicates an Overheat condition when it shouldn’t):
- You can use an ohmmeter to evaluate the validity of each sensor independently (after unplugging the sensors from the circuit board).
- You will need sharp tips on the meter probes(or a Balboa Logic Jumper on a Stick) to be able to make contact with the little bit of metal of each of the two sensor wires visible through a window on the connector.
- The following chart shows what temperatures certain resistance values translate to:
1.5K 231F 110.5C
3.0K 190F 88.0C
5.0K 162F 72.0C
7.0K 144F 62.5C
9.0K 131F 55.0C
10.0K 126F 52.5C
11.1K 121F 49.5C
11.7K 119F 48.5C
12.1K 117F 47.5C
12.7K 115F 46.0C
13.2K 113F 45.0C
13.6K 112F 44.5C
14.1K 110F 43.5C
14.7K 108F 42.5C
15.4K 106F 41.0C
16.2K 104F 40.0C
17.2K 101F 38.5C
18.1K 99F 37.0C
20.2K 94F 34.5C
25.5K 84F 29.0C
30.0K 77F 25.0C
40.0K 65F 18.5C
55.0K 53F 11.5C
95.0K 32F 0.0C
184.0K 9F -13.0C
320.0K -9F -23.0C