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“CHECK SENSOR” indicator on
If the “CHECK SENSOR indicator is on and NOT blinking, there may be a possible open circuit or short
circuit with the pool sensor. Using a voltmeter, measure the DC voltage across the terminals of the pool
sensor as indicated in figure 5. If the voltage is close to zero volts, the sensor has a short to ground. Remove
the sensor from the terminal block and measure the voltage across the pool terminals again. If the voltage
is still close to zero volts, there is an internal short and the unit must be returned for repair. If the voltage
is close to five volts, the pool sensor itself may be at fault.
With the sensor disconnected from the unit, measure the resistance of the sensor using an ohmmeter. At
room temperature (25ºC/77ºF) the sensor should measure approximately 10K ohms (10,000 ohms ± 1%).
For other resistance measurements at different temperatures, consult the table at back of manual. If the
sensor is not returning the correct value, it is defective and will need to be replaced. If the sensor is returning
approximately the correct value, reconnect it to the terminals marked “POOL SENSOR”. If the “CHECK
SENSOR” indicator remains on, the unit is defective and needs to be replaced.
“CHECK SENSOR” indicator blinking
If the “CHECK SENSOR indicator is blinking, there may be a possible open circuit or short circuit with the
solar sensor. Using a voltmeter, measure the voltage across the terminals of the solar sensor. If the voltage
is close to zero volts, the sensor has a short to ground. Remove the sensor from the terminal block and
measure the voltage across the solar terminals again. If the voltage is still close to zero volts, there is an
internal short and the unit must be returned for repair. If the voltage is close to five volts, the solar sensor
itself may be at fault.
With the sensor disconnected from the unit, measure the resistance of the sensor using an ohmmeter. At
room temperature (25ºC/77ºF) the sensor should measure approximately 10K ohms (10,000 ohms ± 1%).
For other resistance measurements at different temperatures, consult the table at back of manual. If the
sensor is not returning the correct value, it is defective and will need to be replaced. If the sensor is returning
approximately the correct value, reconnect it to the terminals marked “SOLAR SENSOR”. If the “CHECK
SENSOR” indicator remains on, the unit is defective and needs to be replaced.
If FREEZE PROTECTION is enabled:
When a sensor is disconnected from the unit and freeze protection has been enabled, the SENSOR FAULT
light will NOT activate. The GL-235 will recognize this as a freeze condition and activate freeze protection.
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