Hot Spring T-Stat Thermistor 2002 Onwards

Hot Spring T‑Stat Control Thermistor (2002 Onwards)

Precision Temperature Sensor for Hot Spring, Tiger River & Limelight Spas (2002+)

This official replacement control thermistor (also known as “T‑Stat”) is engineered for Hot Spring, Tiger River, and Limelight spa models built from 2002 to the present. It functions as the key temperature-reading sensor that helps regulate heater performance in your spa’s control system.

Technical Specifications

• Part Number / OEM: Watkins 39205 (also replaces older OEM # 39530)

• Function: Reads water temperature and communicates to motherboard to control heater operation

• Connector: 4-pin plug at control board end; screw-thread fitting at sensor end

• Probe Housing Diameter (threaded part): 10 mm

• Probe Tip Diameter (ball nose): 6 mm

• Cable Length: ~1,040 mm (41 inches)

Key Features

• New extended housing design allows the probe to sit deeper in the water for more accurate temperature readings

• Designed as a direct replacement for OEM sensors in Hot Spring systems using Intel® IQ2020 electronics

• Compatible with Watkins, Limelight, and Tiger River control thermistor systems manufactured since 2002

Benefits

• Restores heater control functionality—ensures accurate heater on/off and prevents overheat

• Reduces false high-limit shutdowns or flashing error indicators due to sensor issues

• Easy to install: no soldering—just unscrew the old probe, screw in the new one, and plug into the control board

• Durable, OEM-quality construction designed for spa environments

Recommended Use

• Replaces factory control thermistor sensors in Hot Spring IV models

• Ideal during SPA heater servicing, heater conversion, or when troubleshooting blue-blinking heater faults

• Best practice: Replace control thermistor and hi-limit sensor together to ensure consistent performance