EcoStor2™ Solar
ST-I Thermistor Wiring Test Procedure
Thermistor Wire Testing
Step 1. Disconnect and unplug the solar control.
Step 2. Disconnect the thermistor twisted pair from the control or control sensor wiring.
Step 3. Connect a multimeter set to read ohms to the twisted wire stripped ends. Determine the resistance value of the attached thermistor. NOTE: The thermistor is field supplied and various
thermistors have different ohm values for different temperatures. Refer to the temperature specification sheet for the thermistor installed on the water heater to determine if the resistance value is correct.
The image to the side shows a resistance value for a thermistor at ambient temperature connected under the lower access cover (brown twisted pair). The same procedure can be followed to determine if the upper thermistor value is correct.
Step 4. If the multimeter indicates a resistance that does not match the actual temperature of the thermistor, replace the thermistor. Reconnect the wiring, verify that the new thermistor does match, and reconnect to the solar control. Turn on the power to the solar control.
If the multimeter indicates a short or open, disconnect the thermistor from the connection made under the access cover. Measure the thermistor ohm value directly. If the multimeter indicates an open, replace the thermistor.
If the multimeter indicates an appropriate ohm value, determine which wire is open by measuring directly from one end of the wire to the other, or if short; verify by measuring both wire ends from the same location. If the wiring cannot be fixed, the wiring for the thermistor may have to be ran on the outside of the water heater. Replace the wiring, and reconnect it to the solar control. Turn on the power to the solar control.
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