Water Heater Operation - A.O. Smith 300 Series Installation And Operating Manual

Some people are more likely to be permanently injured
by hot water than others. These include the elderly,
children, the infirm and the physically/mentally disabled.
Table 1 (published by U.S. Government Memorandum,
1978) shows the approximate time-to-burn relationship
for normal adult skin. If anyone using hot water provided
by the water heater being installed fits into one of these
groups, special precautions must be taken.
Water Time for 1st
Temperature Degree Burns
°F (Less Severe Burns)
110 (normal shower temp.)
116 (pain threshold)
116 35 minutes
122 1 minute
131 5 seconds
140 2 seconds
149 1 second
154 instantaneous
(U.S. Government Memorandum, C.P.S.C., Peter L.
Armstrong, Sept. 15,1978)
Table 1.
In addition to using lowest possible temperature setting
that satisfies demand of application, a mixing valve
should be installed at water heater (see Figure 7 and
Figure 8) or at hot-water taps to further reduce system
water temperature.
Mixing valves are available at plumbing supply stores. Consult
a Qualified Installer or Service Agency. Follow mixing valve
manufacturer's instructions for installation of the valves.
Before changing the factory setting on the thermostat,
read the "Operating The Temperature Control System"
section in this manual.
12

WATER HEATER OPERATION

Figure 10 shows the water heater's sequence of operation
when a call for heat is initiated. The ignition control module
will attempt to light the burner three times. If the ignition
control does not detect ignition it will enter lockout mode
and flash the corresponding error code.
Time for Permanent
Burns 2nd & 3rd
Degree (Most
Severe Burns)
45 minutes
5 minutes
25 seconds
5 seconds
2 seconds
1 seconds
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HEATER
THERMOSTAT
CALLS FOR
HEAT
HEATER CONTROL
CHECKS TO ENSURE
BLOWER EXHAUST
PRESSURE SWITCH IS
OPEN
BLOWER IS ENERGIZED
CONTROL CHECKS TO
ENSURE: EXHAUST
PRESSURE SWITCH
CLOSES AND INTAKE
PRESSURE SWITCH
REMAINS CLOSED
INDICATING BLOWER IS
OPERATING AND THERE
ARE NO BLOCKAGES
(INTAKE OR EXHAUST)
TEMPERATURE SWITCH
REMAINS CLOSED
INDICATING VENT
TEMPERATURE IS NOT
ABOVE THE ALLOWABLE
LIMIT
Figure 10.
100304526_2000545240 _Rev. 01
IGNITER IS ENERGIZED
AND GAS VALVE IS
OPENED
BURNER COMES ON AND
THE FLAME IS SENSED
BY CONTROL
BURNER CONTINUES
TILL THE WATER IN
THE TANK REACHES
THERMOSTAT SETTING
GAS VALVE IS CLOSED
AND BURNER SHUTS
OFF
BLOWER CONTINUES
FOR A POST PURGE
TIME
HEATER
REMAINS ON
STANDBY UNTIL
NEXT CALL FOR
HEAT