SN1
Caldera Spas
Water Temperature Sensor (Thermistor) Fault
Display shows “SN1” and spa may not heat or may shut down.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed main water temperature thermistor, Loose or corroded thermistor connector at control board, Damaged thermistor wiring harness, Water intrusion into sensor well
How to Fix / Troubleshooting
Safety first: Turn off power at the GFCI breaker before accessing the control box.
- Locate sensor connections: Open the equipment compartment and remove the cover from the IQ control box. Identify the water temperature sensor (thermistor) plug labeled on the board.
- Inspect and reseat: Unplug the thermistor connector, check for corrosion or moisture, then firmly reconnect it. Ensure the wiring is not pinched or damaged.
- Check sensor location: Verify the thermistor is fully inserted into its well on the heater or plumbing and that the retaining clip is secure.
- Power cycle: Restore power and see if the “SN1” code clears after a few minutes.
- If code persists: The thermistor is likely defective. Replace it with a Caldera-compatible temperature sensor, routing the new cable along the original path and securing it away from hot or moving parts.
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Repair Difficulty
Medium
3/5
Required Part
Water Temperature Thermistor
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