A.O. Smith 100 Series Installation And Operating Manual page 39

Note: When there will be no domestic hot water demand for an
extended period of time, the temperature set point should be
set at 90°F to prevent "Stacking" and T&P discharge.
HIGH TEMPERATURE APPLICATIONS
Higher operating temperatures cause more wear on all water heaters
and will decrease the life span of the water heater. Consider installing
a small booster water heater for high temperature applications to
raise the outlet temperature from the larger primary water heater to
the desired point of use temperature. Contact your local distributor
or call technical support phone number listed on the front page of
this manual for further technical assistance.
HIGH TEMPERATURE LIMIT CONTROL (ECO)
This water heater is equipped with an ECO (energy cut out) non-
adjustable high-temperature limit designed to protect against
excessively high water temperatures inside the water heater's
storage tank. The Control board constantly monitors the state of
the temperature sensor thermistors. If the ECO activates due to
abnormally high water temperature (approximately 190°F), the
Control Board will lock out and display fault code E00 on the UIM.
If the ECO activates due to abnormally high water temperatures in
the storage tank, the control system will immediately de-energize the
Gas Control Valve and end current heating cycle. The control system
will lock out disabling further heating operation. It is important that a
Qualified Service Technician be contacted to determine the reason
for ECO activation before resetting the ECO. Once the reason has
been determined and corrected the ECO can be reset as follows:
If the ECO activates, water temperature must drop below 140°F
before the control system can be reset. Once water temperature
has cooled below this point t, the Control Board must be reset. To
reset the Control Board, do the following:
1. Unlock the buttons (by pressing the Lock/Unlock button for 3
seconds), if the interface is locked
2. Simultaneously press the ON/OFF and Plus (SW3) buttons for
3 seconds.
See Figure 42 (page 40) for the button locations..
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