Welcome to Backyardplus! In this post, we are going to show you how to diagnose and replace a bad control T-stat thermistor (temp sensor) on a 1997-Forward Hot Spring spa, Tiger River spa, and Limelight spa. If you have a flashing green ready light on your control panel or a flashing green logo light, it means you probably have a bad temp sensor. Always replace both sensors at the same time. Before we get started, let’s go over the tools and parts you will need.
Table of Contents: How To Diagnose and Replace a Bad Control T-stat Thermistor in a 1997-Forward Hot Spring Spa, Tiger River Spa, and Limelight Spa
Tools you will need:
- Phillips head screwdriver
- Crescent wrench
- Two hose pinching pliers
Parts you will need:
- If you have a 1997 – 2003 Hot Spring or Tiger River spa with the No-Fault 4000 or 6000 heater like the one in this post, the wells for the sensors are shallower than the newer heaters. You will need these shallow well sensors: Thermistor, Control & Hi-Limit Sensor Kit, Item#: 34-01395-K
- All other No-Fault 4kW and 6kW heaters use 79005 and 79006 sensors. Or, if the sensors plug into the outside of the control box, use the 78969 and 78970 sensors.
- Magic Lube Silicone Grease, 1 oz. Tube Item #: ML-1OZ-BYP
Step 1. Disconnect power from the spa.
Step 2. Remove the equipment door.
Step 3. Locate the heater thermistors. You may have to remove the control box to gain access to the control T-stat and Hi-Limit Thermistors.
Step 4. Locate the T-stat sensor. On the IQ 2000, the control T-stat thermistor is located above the Hi-Limit thermistor on the outside of the control box (see photo below). On the 2002-2003 IQ 2020 control box, the control T-stat is located above the Hi-Limit thermistor and plugs directly into to the motherboard.
Unplug the old sensor from the control box and plug the new one in its place.
Step 5. Pinch off both the inlet and outlet heater hoses with your hose pinching pliers.
Step 6. Place a towel underneath the heater to catch the water.
Step 7. Cover the control thermistor O-ring with silicone grease and place it on the sensor.
Step 8. Loosen the control T-stat thermistor with your Crescent wrench by turning it counterclockwise. The T-stat thermistor is located on the inlet side of the heater.
Step 9. Remove the old sensor then immediately place your finger into the opening to prevent water from flooding the equipment compartment.
Step 10. Thread in the new control T-stat thermistor by turning it clockwise. Get it snug with the Crescent wrench but do not over-tighten.
Step 11. Remove the old Hi-Limit thermistor and install the new one.
Step 12. Remove the hose pinching pliers from the heater hoses.
Step 13. Reconnect power to the spa.
If the green ready light is no longer flashing it means you have solved the issue! Good job!
NOTE: If the green ready light continues flashing it means you probably have a bad control head. Make sure your sensors are plugged in correctly. If they’re not, the green ready light or red power light will continue flashing.
Watch the video here “Is Your Green Ready Light or Green Logo Light Flashing? How To Diagnose and Replace a Bad Control T-stat Thermistor in a 1997-Forward Hot Spring Spa, Tiger River Spa, and Limelight Spa!”
Sku: 34-01395-KThermistor, Control & Hi-Limit Sensor Kit, After Market$81.30
Sku: 78969Thermistor, High-Limit, Hot Spring and Tiger River$26.80
Sku: 78970Thermistor, Control Thermostat, Hot Spring and Tiger River$26.80
Sku: 79006Thermistor, Control Thermostat, Watkins No Fault Heater, Hot Spring, Tiger River and Limelight$26.80
Sku: 79005Thermistor, High-Limit, Watkins No Fault Heater, Hot Spring, Tiger River, Limelight$26.80
Sku: ML-1OZ-BYPSilicone Grease, 1 oz. Tube$4.98
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