Service Handbook - AO Smith Water Heaters

Table Of Contents
Table Of Contents .......................................................................... 1
Introduction .................................................................................... 2
Qualifications..................................................................................... 2
Service Warning................................................................................ 2
Service Reminder.............................................................................. 2
Tools Required................................................................................... 2
Installation Considerations ..................................................... 3
Instruction Manual............................................................................. 3
Closed Water Systems ...................................................................... 3
Thermal Expansion............................................................................ 3
Air Requirements............................................................................... 3
Contaminated Air ............................................................................... 3
Venting............................................................................................... 4
General Venting Information....................................................... 4
Maximum Equivalent Length Requirements............................... 4
Intake Air Connection.................................................................. 5
Electrical Requirements..................................................................... 6
Grounding and Polarity............................................................... 6
Power Supply Test ...................................................................... 6
Installation Check List........................................................................ 7
Features And Components ......................................................... 8
Front & Back Views ........................................................................... 8
Top View ............................................................................................ 9
Combustion Blower & Burner Assembly ............................................ 9
Operation and Service ............................................................... 10
How It Works ................................................................................... 10
Combustion Blower..........................................................................11
Burner Assembly ............................................................................. 12
Combustion Blower and Burner Removal....................................... 14
Flame Sensor.................................................................................. 18
Flame Sensing Operation......................................................... 18
Flame Sensing Current Test ...................................................... 19
Igniter ............................................................................................... 20
Igniter Current Test .................................................................... 20
Venturi ............................................................................................. 22
Gas Valve ........................................................................................ 23
Gas Valve Voltage Tests............................................................ 23
Gas Valve Removal................................................................... 24
Gas Pressure ................................................................................... 25
Gas Pressure Test ..................................................................... 26
Gas Flow Test ........................................................................... 27
Pressure Switches........................................................................... 28
Construction & Operation.......................................................... 28
Control System Monitoring........................................................ 29
Pressure Switch Tests ..................................................................... 31
Continuity Test During Standby................................................. 31
Continuity Test During Operation.............................................. 32
Pressure Test During Operation................................................ 32
Temperature Probe.......................................................................... 35
Temperature Sensor Test .......................................................... 35
ECO Continuity Test .................................................................. 36
Control System Hardware......................................................... 37
UIM (User Interface Module)............................................... 37
CCB (Central Control Board).............................................. 39
CCB Cover Removal And Replacement............................. 40
CCB Circuit Board Layout................................................... 41
CCB Connection Identification........................................... 42
Wiring Diagram.......................................................................... 44
Control System Operation ................................................ 45
Overview .................................................................................... 45
Control System Features.................................................... 45
Commercial And Residential Models.................................. 46
Control System Navigation.................................................. 46
User Input Buttons .............................................................. 46
Desktop Screen................................................................... 46
Status Icons ........................................................................ 47
Operating States ................................................................. 48
Control System Menus.............................................................. 48
Temperatures...................................................................... 49
Heater Status ...................................................................... 50
Display Settings.................................................................. 51
Heater Information.............................................................. 51
Current Fault ....................................................................... 52
Fault History ........................................................................ 52
Fault Occurrence ................................................................. 52
Restore Factory Defaults.................................................... 52
Service Contact Information................................................ 53
Sequence Of Operation............................................................. 54
Sequence Of Operation Flow Chart.......................................... 55
Troubleshooting ................................................................... 56
Rough Starting/Rough Operation........................................ 56
Not Enough Hot Water ........................................................ 56
Heater Status Menu............................................................ 56
Things To Check Before Servicing...................................... 56
Resetting The Control System ............................................ 56
Control System Unresponsive................................................... 57
UIM (LCD) Is Blank ............................................................. 57
UIM Is Inoperable................................................................ 57
Fault Messages......................................................................... 58
AC Reversed....................................................................... 58
Temp Probe Open............................................................... 58
Temp Probe Short............................................................... 58
Flame Sensor Short............................................................ 59
Flame Detect Error .............................................................. 59
Energy Cut Out (ECO) ........................................................ 60
Blocked Air Intake ............................................................... 61
Blocked Exhaust................................................................. 62
Blower Prover Failure.......................................................... 62
Blower Prover Open............................................................ 63
Low Igniter Current.............................................................. 64
Ignition Failure..................................................................... 65
Communication Failure....................................................... 66
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