A.O. Smith 401 Water Heater User Manual


 
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Menu Screen:
Displayed when the user presses the "Menu" key. This screen is
the selection point for the other 9 screens.
Temperature Screen:
Displays the sensed temperatures of the Outlet, Inlet, and Tank
probes. Also displayed is the calculated Delta T (Outlet minus
Inlet) for the system. Shorted ("Short") and disconnected ("----")
probes are also displayed.
System Status Screen:
This screen is used to view the status of switch inputs and output
states. An asterisk (*) is displayed next to the label when the
status is "True" (the description is fulfilled). For example, if water
is flowing, or detected by the flow sensor, then an "*" will appear
in front of the Flow label (i.e. *Flow). Another example would be
the ECO switch. If the outlet temperature is too high the display
will show: *ECO.
NOTE: The LWCO, IRI Gas Valve, Powered Vent, High Gas, and
Low Gas inputs are optional inputs. Flame sensing, Igniters, and
Blowers are optional on Stages 2, 3 and 4. (Except on a 4-stage
system, stage 2 always has an Igniter, Blower, and Flame Sensor.
Those dipswitches on stage 2 are not relevant.) One or two speed
blowers can be used on any stage.
The System monitors the inputs at these times:
ECO, LWCO, Blocked Flue, Low Gas, Hi Limit, and Hi Gas - at all
times for a fault condition.
Tstat - at all times for open/closed conditions.
IRI Gas and Powered Vent - for an on condition when their outputs
(Pump, IRI Gas Pwr, Powered Vent Power) are turned on and an
off condition at all other times.
Flow-for an on condition when the pump is on (no check for off state)
Blower Prover - when the Blower is on.
Igniter Current - for an on condition approximately 18 seconds
after the Igniter is turned on until the igniter is turned off and an
off condition at all other times.
Flame - for an on condition approximately 5 seconds after the
gas valve is turned on until the valve is turned off and at all other
times for an off condition.
Control Status Screen:
Displays the status that the CCB and FCB micros are in. The CCB
has 5 possible states and the FCB's have 9. The normal CCB states
sequence is to move from Idle, to Pre-Circulate, then to Heating
Stage 1-2-3-4 when a call for heat is initiated. Once heat has been
satisfied or the Thermostat is opened, the sequence moves to Post-
Circulate and then back to Idle. If a fault occurs at any time, the
process jumps out of sequence and goes directly to the appropriate
Hard or Soft Fault state.
Description of CCB control states:
Idle:
The yellow "Standby" LED is turned on and the system waits for
a heat request (determined by the Thermostat or controlling probe
inputs). All outputs are off in this state except that if the Post-Circulate
time is set to continuous, the pump will be on. When the heat request
is received, the system moves to the Pre-Circulate state.
Pre-Circulate:
The yellow LED is turned off and the green "Running" LED is
turned on. The green LED will remain on for all other states
except the fault states. If enabled the powered vent and the IRI
gas valve are turned on. A command is sent to all active stages
to cold purge the system. Cold purging clears out any
combustion gas that may be in the combustion chamber. When
purging is complete the system moves to the Heat State.
Heat Stages 1-2-3-4:
The system will command the FCB micros to start their heat
sequence starting with stage 1. Stage 2, 3, 4 will be activated in
order based on an algorithm that determines how much heat is
needed. The system will remain in this state until the heat request
is satisfied, the Tstat is opened, or a fault occurs.
The following status information is displayed from the
System Status Screen:
Status Displayed *(True Condition) Input Output
ECO Outlet temperature too high open - - - -
LW/CO Water Level low open - - - -
Blk Flue Flue blocked open - - - -
Flow Water flowing closed - - - -
Low Gas Gas pressure low open - - - -
Tstat Thermostat requesting heat closed - - - -
Hi Limit Outlet temp exceeds High Limit setpoint - - - - - - - -
Pump Pump output activated - - - - On
IRI Gas Pwr IRI output relay activated - - - - On
IRI Gas IRI Gas Valve on closed - - - -
Pwr Vent Power Vent running closed - - - -
Alarm Alarm output activated - - - - On
Pwr Vent Pwr Power Vent output relay activated - - - - On
- - - - STAGES 1 to 2 - - - -
BlwHi Prv Blower pressure sufficient closed - - - -
Blw Hi Blower High output activated - - - - On
BlwLo Prv Blower pressure sufficient (not used at this time) closed - - - -
Blw Lo Blower low output activated (not used at this time) - - - - On
Ignt Cur Igniter current sufficient for ignition - - - - - - - -
Ignit Igniter output is activated - - - - On
Gas Relay Gas output relay activated - - - - On
Hi Gas Gas pressure too high open - - - -
Flame Flame detected - - - - - - - -