Spa & Hot Tub Troubleshooting
Problem: The temperature displayed on the topside controller doesn't match spa water temperature measured by a separate calibrated thermometer.
Make sure the pump that circulates water through the heater is "ON" for at least 10 minutes before you compare temperatures between our controller’s temperature sensor and your thermometer.
General Information About How Spas Are Made
All hot tubs by design must be equipped with two temperature sensor circuits. One is called a Hi Limit sensor (HLM) and the second one is the Temperature sensor (SENS). The Hi Limit circuit is designed to shut power “OFF” through the open Neutral relay if the temperature where the Hi Limit sensor is located exceeds 112°F (50°C). The Temperature sensor (SENS) senses and displays the spa water temperature at the location where the sensor is inserted. It also allows the consumer to set the desired water temperature from 45°F (7.2°C) to 104°F (40°C). On most spa controls, the Hi Limit sensor and the Temperature sensor are located on the heater manifold. However, some spas have their temperature sensor located on the spa shell and the Hi Limit located on the heater manifold. When comparing the displayed temperature to your thermometer, you must insert your thermometer near where the temperature sensor is located on your spa otherwise the comparison may not be accurate.
Explanations and Solutions
If the Temp and Hi Limit sensors are located on the heater manifold:
The heater manifold is located inside the spa cabinet. If the sensors are located at the heater manifold, the Temperature Sensor senses the water temperature inside the heater manifold (near the heater element), displays the temperature it senses on the top display, and commands the heater circuitry accordingly. In many spa applications especially during winter, the temperature inside the spa cabinet where the control and heater are located will be different (usually lower) than the water temperature inside the hot tub. When the pump is not circulating water through the heater manifold, the temperature of the water volume inside the heater manifold (approximately 0.3 gallons [1.2 liters]) may drop a lot faster than the temperature of the water volume inside the hot tub (200+ gallons [750+ liters]). In addition, the back of the spa shell is insulated with several inches of foam, but the spa cabinet itself may not be insulated (or poorly insulated). Cold air penetrates through the spa cabinet and lowers the temperature of the pipes including the heater manifold where the sensors are located. The Temperature sensor will display the temperature it is sensing in the heater manifold. If the pump is OFF and not circulating water through the heater housing the temperature inside the heater housing will continue to drop quickly. Once the temperature drops 15 to 20 degrees below the desired temperature setting, the freeze guard circuitry will energize the low pump circuitry continuously.
If the spa cabinet is not well insulated, when the pump is "OFF", the temperature inside the heater manifold may drop much faster than the temperature of the water in the hot tub itself.
To check the temperature accuracy:
- Turn the circulating pump "ON" for 15 minutes.
- Using a separate, properly calibrated thermometer, measure the temperature at the heater manifold and compare it to the display.
- If the measured temperature is within +/-5°F (9°C) of the displayed temperature.
Solution A: Use the calibration "CALB" procedure on our controller and calibrate the Temperature sensor to match your thermometer.
- If the measured temperature is >10°F (18°C) of the displayed temperature.
Solution B1: Try to better insulate your spa cabinet.
Solution B2: Change the location of the Temperature sensor to be inside the spa shell (you risk losing freeze protection at the heater manifold).
Solution B3: You may need to change the Temperature sensor, or very rarely, the PC Board.
The opposite can occur during summer time if the spa cabinet is not well ventilated.
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Displayed Temperatures Don't Match
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