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Servicing should only be performed by a Qualified Service Agent
37
OPERATION & SERVICE
IMMERSION TEMPERATURE PROBE
This section of the manual provides
information on how test the Immersion
Temperature Probe on Electronic Control
Models - see Figure 2 on page 9 for
location. The Immersion Temperature
Probe contains the ECO (energy cut out)
and a Temperature Sensor. The Immersion
Temperature Probe plugs into the CCB
circuit board at the J5 socket. See the CCB
circuit board layout and identification
illustration and tables on pages 42 - 44.
ECO High Temperature Limit Switch
The ECO (energy cut out) is a high
temperature limit switch designed to protect against excessively high water temperatures
inside the water heater. The ECO is a normally closed switch located inside the Immersion
Temperature Probe (two red wires). The ECO temperature setting is non adjustable; the
contacts open at 202°F/94°C and will close at approximately 140°F/60°C.
The control system constantly monitors the state of the ECO switch contacts. If the ECO
activates (contacts open) due to abnormally high water temperature the control system will
lock out and display a “Energy Cut Out (ECO)” Fault message on the UIM (page 49).
Voltage to the contactor coils (page 32) and heating elements is terminated to prevent
further heating operation.
Should the ECO activate, the water temperature must drop below 140°F/60°C before the
control system can be reset. Once the water temperature has cooled below this point the
power supply to the water heater must be turned off and on again to reset the control
system.
Temperature Sensor
The temperature sensor located inside the Immersion Temperature Probe is a “thermistor”
(two black wires). Thermistors are thermally sensitive resistors. As the water temperature
rises the resistance (in ohms) of the sensor will decrease; as the temperature falls the
resistance will increase - see the Temperature Sensor Resistance Data table on page 38.
The control system interprets the changes in resistance as changes in water temperature.
The control system constantly monitors the temperature sensor (thermistor) for temperature.
The control system is also programmed to declare a Fault condition if the resistance of the
temperature sensor drops below 390 ohms (shorted) or above 56,000 ohms (open).
If the resistance of the temperature sensor is below 390 ohms the control system will lock
out and display a “Temp Probe Short” Fault message on the UIM (page 49). If the resistance
of the temperature sensor is above 56,000 ohms the control system will lock out and display
a “Temp Probe Open” Fault message on the UIM. Voltage to the contactor coils (page 32)
and heating elements is terminated during lock out to prevent further heating operation.
If the control system locks out the condition that caused the lock out must be corrected
before the control system can be reset by cycling power off and on again.
Immersion Temperature Probe