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Tr oubleshooting (cont’d)
CAUTION
This will not discontinue power from the water
heater.
THERMOSTAT DIAGNOSTICS
The programmable thermostat will use the upper and lower
temperature sensors (thermistors) to determine when either
the upper or lower heating element is not functioning. It can
also detect a faulty temperature sensor. The thermostat will use
the service icon and its associated codes to indicate the specific
failure condition and will also save the last failure condition.
To display the last failure, depress and hold the
up ( ) arrow
or the down ( ) arrow
button for 4 seconds while in the nor-
mal run mode. Be Careful; depressing the “ERASE” button
while the last failure is displayed will erase the stored failure.
1. No Water/Dry Fire Warning – If the sensors indicate a
rise in temperature greater than 50°F in the first minute
after power-up, the control will display a “NO WATER”
icon indicating that there is no water in the tank. This will
immediately shut off power to both elements.
2. Upper Temperature Sensor Failure – If the upper sensor is
either open or shorted, the “SERVICE” icon and the let-
ters “U” and “S” will be displayed. The thermostat will
then use only the lower heating element and lower temper-
ature sensor to control the water temperature until the
upper sensor has been replaced.
4. Upper Element Failure – Tests after 90 minutes of contin-
uous upper element heating without an increase in upper
water temperature. The thermostat turns off the upper ele-
ment and tries for 30 minutes to raise the temperature of
the upper sensor using the lower element. If the upper tem-
perature sensor rises using the lower element, the upper ele-
ment will again be tried. After 30 minutes, if the upper ele-
ment does not raise the upper water temperature on the
second attempt, then an upper element failure will be indi-
cated by displaying the “SERVICE” icon and the letters
“U” and “E”. The lower element will only be used to heat
the water until the upper element has been replaced.
5. Lower Element Failure – After 120 minutes of continuous
lower element heating without an increase in lower water
temperature, lower element failure will be indicated by dis-
playing the “SERVICE” icon and the letters “L” and “E”.
Replace the lower heating element.
6. High Limit Device Failure – If a lower element failure
occurs when the upper element has also failed, the thermo-
stat will determine that the high limit device has failed.
High limit device failure will be indicated by displaying the
“SERVICE” icon and the letter “C”. Replace the high
limit device.
7. Re-Check – The system will run a failure event sequence
three (3) times before it assumes a final service code.
3. Lower Temperature Sensor Failure – If the lower sensor is
either open or shorted, the “SERVICE” icon and the let-
ters “L” and “S” will be displayed. The thermostat will then
use only the upper heating element and upper temperature
sensor to control the water temperature until the lower sen-
sor has been replaced.
Operational Conditions (cont’d)