E03 error code appears and the heater shuts off; water temperature reading seems incorrect or unstable.

Safety first: Unplug the spa before inspecting any internal components. Hot water can cause burns; allow water to cool if necessary.

• Power cycle: Unplug the spa for 10 minutes, then reconnect and try again to rule out a temporary logic fault.
• Compare temperature: Use an external pool thermometer to compare actual water temperature with the displayed temperature. A large difference suggests a sensor issue.
• Descale heater path: If you have hard water, mineral scale can insulate the sensor. Run a spa descaling treatment following SaluSpa’s chemical guidelines, then flush and refill.
• Check for kinks or damage: On some models, the sensor wiring harness is visible where it enters the heater housing. Inspect for crushed, cut, or chewed (rodent) wiring.
• Test again: After cleaning and refilling, restart the spa. If E03 persists, the NTC sensor or main PCB is likely defective and the pump/heater unit or sensor assembly may need replacement.

Warning: Replacing internal sensors usually requires opening the sealed pump/heater housing. This should be done only by a qualified technician or by replacing the entire pump/heater assembly.