Sn1
Coast Spas
Water Temperature Sensor Failure
Display shows Sn1, SN1, or SENSOR 1 error; 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
Open or shorted temperature sensor probe, Corroded sensor connector at control pack, Damaged sensor cable from rodent or abrasion, Failed A/D input on control board
How to Fix / Troubleshooting
Safety first: Turn off power at the breaker before accessing the control pack or sensors.
- Locate the temp sensor: On most Coast Spas, the water temperature sensor is threaded into the heater tube or mounted in a thermowell in the spa shell.
- Inspect wiring and plug: Check the sensor cable for cuts or chew marks. Reseat the sensor plug on the control board, ensuring correct orientation.
- Compare temperature reading: If the topside shows an obviously incorrect temperature (e.g., 32°F or 118°F when water is lukewarm), the sensor is likely faulty.
- Replace sensor: Unscrew the old sensor from the heater tube (have towels ready for minor water loss) and install the new Coast Spas-compatible sensor with the supplied O-ring. Do not overtighten.
- Retest: Restore power and verify that Sn1 is cleared and temperature reads correctly.
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Repair Difficulty
Medium
3/5
Required Part
Temperature Sensor
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