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Sn3 on a Hydro-Quip hot tub: temperature sensor fault

The water temperature sensor circuit is open or shorted, so the heater is disabled. Check the real water temperature before using the tub.

Also shown as: SN3, Sn 3

Most likely causes

  1. 1Failed temperature sensormost likely
  2. 2Loose or corroded sensor plugcommon
  3. 3Damaged sensor wirecommon
  4. 4Circuit board faultless common

What to try, in order

  1. Reset power at the breaker for 30 seconds.
  2. Check the water with a floating thermometer.
  3. With power off, look for damaged sensor wiring in the equipment bay.
  4. Arrange a sensor test and replacement.

Sn3 questions

What is the difference between Sn1 and Sn3?

Sn1 is the hi-limit safety sensor on the heater. Sn3 is the sensor that reads the water temperature.

Is the temperature sensor hard to replace?

The part is simple, but it plugs into the circuit board, so it is a job for a technician.

Related codes

Hydro-Quip FLO · Flow or pressure switchHydro-Quip OH · Overheat protectionHydro-Quip Sn1 · Hi-limit sensor fault

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