Temperature Regulation; High Temperature Limit Control (Eco); Thermostat Control - A.O. Smith 300 Series Instruction Manual

HIGH TEMPERATURE LIMIT CONTROL (ECO)

This water heater is equipped with an ECO (energy cut out) non
adjustable high temperature limit switch. The ECO is a normally
closed switch that opens (activates) on a rise in temperature.
The ECO is located inside the Temperature Probe (two red wires).
See Figure 3 (page 10) and Figure 4 (page 11). The ECO
switch contacts will open when the water temperature reaches
approximately 202°F (94°C) and close at approximately 140°F
(60°C).
If the ECO activates (contacts open) due to abnormally high water
temperatures in the storage tank the control system will immediately
de-energize the 24-volt gas valve and end the current heating cycle.
The control system will "lock out" disabling further heating operation.
The control system will display the "Energy Cut Out (ECO)" Fault
message on the LCD screen. It is important that a Qualified Service
Agent be contacted to determine the reason for the 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, 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.

THERMOSTAT CONTROL

Hot water temperatures required for automatic dishwasher and
laundry use can cause scald burns resulting in serious personal
injury and/or death. Table 11 on page 36 shows the approximate
time-to-burn relationship for normal adult skin.
The temperature at which injury occurs varies with the person's age
and duration of exposure. The slower response time of children,
the elderly or disabled persons increases the hazards to them. If
anyone using hot water provided by the water heater being installed
fits into one of these groups or if there is a local code or state law
requiring a certain water temperature at the point of use, then special
precautions must be taken.
To reduce the risk of unusually hot
water reaching the fixtures in the
house, install thermostatic mixing
valves at each point of use.

TEMPERATURE REGULATION

TEMPERATURE REGULATION
Water temperature over 125°F (52°C)
can cause severe burns instantly
resulting in severe injury or death.
Children, the elderly and the
physically or mentally disabled are at
highest risk for scald injury.
Feel water before bathing or
showering.
Temperature limiting devices such as
mixing valves must be installed
when required by codes and to
ensure safe temperatures at fixtures.
Burn Hazard
In addition to using the lowest possible temperature setting that
satisfies the demand of the application a mixing valve can be installed
at the water heater or at the hot water taps to further reduce system
water temperature.
Never allow small children to use a hot water tap or draw their own
bath water. Never leave a child or disabled person unattended in a
bathtub or shower.
The water heater should be located in an area where the general
public does not have access to set temperatures.
Setting the Operating Set Point at 120°F (49°C) will reduce the risk
of scalds.
Table 10. Time to Burn at Different Temperatures
Water Temperature
°F (°C)
110 (43.3)
116 (46.7)
116 (46.7)
122 (50)
131 (55)
140 (60)
149 (65)
154 (67.8)
(U.S. Government Memorandum, C.P.S.C., Peter L. Armstrong,
Sept. 15, 1978)
The water heaters covered in this manual are equipped with an
electronic control system to regulate water temperature inside the
storage tank. The control system senses temperature from a factory
installed temperature probe in the top of the storage tank. See Figure
3 (page 10) and Figure 4 (page 11) for location.
The "Operating Set Point" is adjusted to regulate water temperature
inside the storage tank. This is an adjustable user setting in the
control system's Temperatures Menu. This and all control system
menus are accessed through the user interface module (UIM) located
on the front of the water heater. See Figure 45 (page 41).
The Operating Set Point is adjustable from 90°F (32°C) to 160°F
(71°C). The factory setting is 120°F (49°C). See Operating Set Point
and Differential Adjustment (page 43) for instructions on how to adjust
the Operating Set Point and other user settings.
Set the Operating Set Point at the lowest setting that produces
an acceptable hot water supply. This will always provide the most
energy efficient operation.
38
Time for Permanent
Time for 1st Degree
Burn
2nd & 3rd Degree
(Less Severe Burns)
(Most Severe Burns
(normal shower temp.)
(pain threshold)
35 minutes 45 minutes
1 minute 5 minutes
5 seconds 25 seconds
2 seconds 5 seconds
1 second 2 seconds
1 second
instantaneous
Burn Hazard
To reduce the risk of unusually hot
water reaching the fixtures in the
house, install thermostatic mixing
valves at each point of use.
Burns