Marquis Spas
Temperature Regulation / Sensor Calibration Issue
Water temperature fluctuates widely or does not match the set temperature.
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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
Aging or drifting temperature sensor, Poor water circulation around sensor, Incorrect sensor installation, Control board calibration drift
How to Fix / Troubleshooting
Safety first: Turn off power at the GFCI breaker before handling sensors.
- Verify with external thermometer: Place a reliable thermometer in the spa water and compare to the displayed temperature.
- Check circulation: Ensure that the circulation pump is running properly so water around the heater and sensors is representative of the whole spa.
- Inspect sensor installation: Confirm that M7 sensors are fully threaded into the heater tube and making good thermal contact.
- Replace sensor pair: If the displayed temperature is consistently off by more than a few degrees, replace the M7 sensor pair with Marquis-compatible parts.
If temperature swings remain large after sensor replacement, the control board may have a regulation issue and should be evaluated.
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Repair Difficulty
Medium
3/5
Required Part
M7 Temperature Sensor Pair for Marquis/ Balboa Heater
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