Specifications

31
A. O. Smith Water Products Service Handbook
Ashland City, Tennessee 2005
©
Training Department
SEQUENCE OF OPERATION
3 STAGE MODELS - TEMPERATURE/STAGE LADDER EXAMPLE
Condition:
Central control Board (CCB) dip switch settings:
SW1-A Set to "Off" (3 Stage)
SW1-C-Set to "Off" (no IRI gas valve in use)
SW1-E-Set to "On" (external thermostat in use)
All other switches either "On" or "Off"
CCB Responsibility:
Staging ICB's
Monitor Safety Limit Devices
Control Circulating Pump
Power Vent (if equipped)
Alarm output (if equipped)
IRI gas valves (If equipped).
Temperature sense from inlet; outlet; tank probe or 24V tank thermostat
SW 1 OFF ON SELECTION:
A 3 Stage 4 Stage Either 3 or 4 stage system
B 3 Trials 1 Trial Either 3 or 1 trial(s) for ignition
C No IRI gas valve IRI gas valve Whether system is IRI or standard
D Inlet Tank Inlet or tank
as controlling probe
E No external TSTAT External TSTAT Whether external TSTAT is used
F Outlet 210° F Outlet 240° F Outlet maximum temperature
G 190° F 220° F Maximum set-point temperature
H Degrees F Degrees C Either °F or °C for displayed temp.
CONFIGURATION SW ITCH TABLE
External 24V Temperature Control
1 Circulation pump “ On”
3 Blowers “On”
4 Power vent “ On”
5 All ignition control boards ( ICBs ) in prepurge state
Pre-Purge, 30 seconds, ends
Combustion blowers – Except Stage 1 - Off
Stage 1 – Igniter “On”
Igniter draws 2.7 Amps
Stage 1 – Main flame sensed
Min. 1 micro Amp (1
µ
A)
No Yes
Igniter off
Stage 2
2
Igniter “On”
3 Igniter draws 2.7A
4 Gas valve open
5 Flame Senser
No Yes
Stage 3
1 Blower “On” - Proves
2 Igniter “On”
3 Igniter draws 2.7A
4 Flame Proves
No Yes
System operates until external thermostat/thermistor reaches set point
2 Flow Switch Closed
Stage 1 Gas Valve
Open – 4 Sec. Trial
Gas Valve Closed
15 Second Interpurge
If Dip Switch “B” Is Set
To “Off”, Retrial for Ignition
1 Blower 2 – “On” Proves Draft
On stages without blowers
or igniters, a retry will occur
after a 5 second interpurge.
System operates until external thermostat reaches set point