Balboa · BP series (TP400, TP600, TP800, TP900, spaTouch panels)Fix soon

SNSR A on a Balboa hot tub: sensor a or b fault

A temperature sensor or its circuit has failed (M031 is Sensor A, M032 is Sensor B) and the spa has shut down. The tub will not heat or run normally until the sensor is replaced.

Also shown as: SNSR B, M031, M032, Sensor A Fault, Sensor B Fault

Most likely causes

  1. 1Failed temperature sensormost likely
  2. 2Loose or corroded sensor plugcommon
  3. 3Sensor cable damaged by rodents or heatcommon
  4. 4Circuit board faultless common

What to try, in order

  1. Reset power at the breaker for 30 seconds.
  2. With the power off, look over the visible wiring in the equipment bay for chewed or pinched cables. Leave the control box closed.
  3. Write down which sensor the panel names (A or B) and the pack model number.
  4. Arrange for the sensor to be tested and replaced.

SNSR A questions

What do M031 and M032 mean?

M031 is a Sensor A fault and M032 is a Sensor B fault. Each means that sensor or its wiring has failed.

Will my tub freeze with a sensor fault?

It can in cold weather, because the spa is shut down. Keep the cover on and put a safe heat source in the equipment bay until it is repaired.

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.