A.O. Smith BTH 120, Service Handbook

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TABLE OF CONTENTS
INTRODUCTION .......................................................................................2
Qualifications ........................................................................................2
Service Warning ...................................................................................2
Service Reminder .................................................................................2
Tools Recommended ............................................................................2
INSTALLATION CONSIDERATIONS ........................................................3
Instruction Manual ................................................................................3
Closed Water Systems .........................................................................3
Thermal Expansion ...............................................................................3
Air Requirements ..................................................................................3
Contaminated Air ..................................................................................3
FEATURES AND COMPONENTS ............................................................4
Combustion Blower & Burner Assembly ...............................................4
Top View: BTH 120 - 250 Models .........................................................5
Top View: BTH 300 - 500 Models .........................................................5
SEQUENCE OF OPERATION FLOW CHART ..........................................6
FAULT AND WARNING CODES ...............................................................7
1. Low Gas Pressure ............................................................................7
High Altitude .................................................................................7
Gas Pressure Specifications ........................................................7
Gas Supply Systems ....................................................................8
Supply Gas Regulator ..................................................................8
Gas Pressure Test ........................................................................9
2. Blower Operation Error ...................................................................11
Pressure Switches .......................................................................11
Control System Monitoring ...........................................................11
Pressure Switch Tests ..................................................................12
Continuity Test During Standby ....................................................12
Continuity Test During Operation .................................................13
Pressure Test During Operation ...................................................13
Pressure Switch Settings .............................................................14
3. Blower Prover Open .......................................................................16
4. Ignition Failure ................................................................................17
5. Blocked Air Intake ...........................................................................20
6. Blocked Exhaust .............................................................................21
7. Flame Sensor Error ........................................................................22
Gas Control Valve ........................................................................22
Gas Control Valve Voltage Tests ..................................................23
Flame Sensor ...............................................................................24
Flame Sensing Operation ............................................................24
Flame Sensing Current Test .........................................................25
8. No Water .........................................................................................26
Powered Anodes ..........................................................................26
Power anode cleaning and removal .............................................26
9. Anode Shorted ................................................................................28
10. Temperature Probe Short (Upper or Lower) .................................29
Temperature Probe ......................................................................29
Temperature Sensor Test .............................................................30
ECO Continuity Test .....................................................................30
11. Temperature Probe Open (Upper or Lower) .................................32
VENTING .................................................................................................33
General Venting Information ........................................................33
INTAKE AIR CONNECTION ....................................................................34
ELECTRICAL CONNECTIONS – ALL MODELS .....................................35
Electrical Wiring ..................................................................................35
Power Supply Connections ................................................................35
Enable/ Disable Switch .......................................................................36
Power Supply Test ..............................................................................36
INSTALLATION CHECK LIST .................................................................37
OPERATION AND SERVICE ..................................................................38
How It Works ......................................................................................38
Combustion Blower ............................................................................38
Modulation ..........................................................................................38
BLOWER SPEED CONTROL – BTH 300 THRU 500 .............................40
VARIABLE FREQUENCY DRIVE – BTH 300 THRU 500 ........................41
BURNER ASSEMBLY .............................................................................42
COMBUSTION BLOWER AND BURNER REMOVAL/ INSTALLATION
INSTRUCTIONS ......................................................................................43
SPARK IGNITER .....................................................................................44
GAS ORIFICE - BTH 300 THRU 500 MODELS ......................................46
Orifice Chart - BTH 300 thru 500 Models ...........................................46
CCB (CENTRAL CONTROL BOARD) .....................................................47
CCB Cover Removal And Replacement .............................................48
CCB Circuit Board Layout ..................................................................49
CCB Connection Identification ............................................................50
WIRING DIAGRAM – BTH 120 THRU 250 .............................................52
WIRING DIAGRAM – BTH 300 THRU 500 .............................................53
CONTROL OVERVIEW ...........................................................................54