Hydro-Quip · Hydro-Quip digital control systemsFix soon

Sn1 on a Hydro-Quip hot tub: hi-limit sensor fault

The hi-limit sensor circuit is open or shorted, so the heater is disabled. The tub will not heat until the sensor is replaced.

Also shown as: SN1, Sn 1

Most likely causes

  1. 1Failed hi-limit 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. With power off, check visible sensor wiring in the equipment bay for damage. Leave the control box closed.
  3. Record the control system model from its label.
  4. Have the sensor tested and replaced.

Sn1 questions

What does Sn1 mean?

It is a fault in the hi-limit sensor, the safety sensor mounted on the heater.

Can I use the tub with Sn1?

The heater is off, so the water will cool. Pumps may still run, but get it repaired soon, especially in winter.

Related codes

Jacuzzi / Sundance Sn1 · Hi-limit sensor faultHydro-Quip FLO · Flow or pressure switchHydro-Quip OH · Overheat protectionHydro-Quip Sn3 · Temperature sensor fault

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