Balboa · VS / GS seriesFix soon

Snb on a Balboa hot tub: sensor b fault

The sensor plugged into the Sensor B jack is not giving a valid reading, and the spa has shut down. It is the same kind of fault as SnA, on the other sensor.

Also shown as: Sb, SnB, Sn b, sensor B

Most likely causes

  1. 1Failed temperature sensormost likely
  2. 2Loose or corroded sensor plug at the boardcommon
  3. 3Damaged sensor cablecommon
  4. 4Fault on the circuit boardless common

What to try, in order

  1. Reset power at the breaker for 30 seconds and see if the code returns.
  2. With the power off at the breaker, check the visible sensor wiring in the equipment bay for damage. Do not open the control box.
  3. Write down the control pack model from its label.
  4. If the code persists, have the sensor tested and replaced.

Snb questions

What does Snb mean on a hot tub?

It means Sensor B, one of the two temperature sensors on the heater, has failed or lost its connection. The spa shuts down as a precaution.

Should I replace both sensors at once?

It is common to replace them as a pair because they are the same age and the system compares one against the other.

Related codes

Balboa -- · Temperature not yet knownBalboa CHEK PH · Maintenance reminderBalboa CLN FLTR · Filter reminderBalboa CNFG FAIL · Configuration errorBalboa dr · Heater may be dryBalboa dry · Heater is dryBalboa Ecn · Economy modeBalboa FLO · Low water flow

General guidance. Follow your manufacturer's instructions; anything inside the control box is work for a licensed professional. Updated October 5, 2026.