A.O. Smith BTX-100 Service Handbook
Commercial / residential gas water heaters
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Summary of Contents for A.O. Smith BTX-100
- Page 1 2008 COMMERCIAL / RESIDENTIAL GAS WATER HEATERS SERVICE HANDBOOK ULTRA HIGH EFFICIENCY POWER VENT / POWER DIRECT VENT FOR MODELS: • BTX-100 • GDHE-50 PRINTED 0308 198142-000...
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Page 2: Table Of Contents
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT SERVICE MANUAL Technical Literature Department ©2008 TABLE OF CONTENTS INTRODUCTION ............2 TROUBLESHOOTING...........41 Qualifications ............2 Rough Start - Rough Operation ....13 and 41 Service Warning ............2 Heater Status Menu ..........33 Important Service Reminder ........2 Things to Check Before Servicing ....41 Instruction Manual ............ -
Page 3: Introduction
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL INTRODUCTION This Service Manual is designed to be an aid in servicing and troubleshooting the 96% thermally efficient, 50 gallon, 100,000 Btu/hr residential and light duty commercial power vent - power direct vent model water heaters listed on the cover of this manual.The instructions, illustrations and procedures contained in this manual are used to verify proper operation and to diagnose and repair common service problems. -
Page 4: Instruction Manual
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL INSTRUCTION MANUAL Have a copy of the Instruction Manual that came with the water heater on hand for the correct model water heater you are working with before servicing. Installation information given in this Service Manual is not a complete installation instruction. -
Page 5: Installation Considerations
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL INSTALLATION CONSIDERATIONS INSTRUCTION MANUAL Installation information given in this Service Manual is not a complete installation instruction. Installation information covered in this Service Manual has a limited focus as it applies to servicing. -
Page 6: Air Requirements
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR REQUIREMENTS Carefully review the requirements for combustion and ventilation air in the Instruction Manual that came with the water heater. Failure to meet these requirements when the water heater is installed or overlooking their importance when servicing the water heater often results in needless down time, unnecessary parts replacement, and customer dissatisfaction. -
Page 7: Venting
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL VENTING The venting information presented in this Service Manual is not a complete venting installation instruction. Refer to the Instruction Manual that came with the water heater for complete installation instructions. The water heater covered in this Service Manual may be installed as a conventionally vented water heater or as a direct vent water heater. - Page 8 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL VENTING (CONT) Pipe Size Requirements Ensure the correct size pipe has been used for the overall equivalent length of the vent and intake air piping installed. Longer equivalent lengths require larger pipe sizes, see Table 1. Maximum Elbow Requirements Three and four inch vent and intake air pipe installations allow a maximum of 6 - 90°...
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Page 9: Electrical Requirements
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL ELECTRICAL REQUIREMENTS The water heater covered by this Service Manual must be grounded in accordance with the local codes, or in the absence of local codes: the National Electrical Code (NFPA 70) or the Canadian Electrical Code (C22.1). -
Page 10: Operation & Service
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL OPERATION & SERVICE HOW IT WORKS This section of the Service Manual will cover operation, common service procedures and water heater construction. The water heater covered in this Service Manual has a helical coil shaped heat exchanger that is submerged in the storage tank. -
Page 11: Blower
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL BLOWER The blower is an assembly consisting of the blower housing, motor and an integrated VFD (variable frequency drive). Blower operation is controlled by the CCB (central control board - page 35). The CCB sends 120 VAC to the Blower/VFD assembly high voltage 3 pin socket. -
Page 12: Burner
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL BURNER The images below show a complete blower/burner assembly removed along with a top view of the water heater with the blower removed. Service Notes - Burner (Flame Sensor) The burner installed in the water heater is a radial fire burner. Radial fire burners can trap debris that enter the blower. - Page 13 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL BURNER (CONT) Burner & Blower Removal The burner should be removed and inspected whenever service is being performed for rough operation or ignition failure. Radial fire burners like the one used on this water heater can trap debris, see Service Notes - Venting on page 7.
- Page 14 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL BURNER (CONT) Burner/Blower Removal (cont) BLOWER/BURNER REMOVAL PROCEDURE (CONT) 9 Remove 4 blower adapter 1/4” hex machine screws. Do not over tighten when reinstalling - torque should not exceed 40 inch lbs. 1/4”...
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Page 15: Venturi
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL VENTURI A Venturi is connected to the inlet of the blower. All combustion air flows through the Venturi. The outlet of the 24 VAC gas valve connects directly to the side of the Venturi. Fuel gas flows from the outlet of the gas valve into the side of the Venturi directly. -
Page 16: Gas Valve
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL GAS VALVE The outlet of the gas valve is connected by flange directly to the side of the Venturi (page 14). There is no manifold gas line on the water heater. A gas orifice with gasket is fitted into the gas valve’s outlet flange. -
Page 17: Gas Pressure Testing
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL GAS PRESSURE TESTING The water heater covered in this Service Manual is rated at 100,000 Btu/hr input. It is certified for elevations up to 10,100 feet (3079 meters) without adjustment. Call the technical support phone number shown on the water heater labeling before operating the water heater at higher elevations. - Page 18 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL GAS PRESSURES (CONT) CHECKING GAS PRESSURES (CONT) 5 Open the supply gas shut off valve - restore Typical manifold and supply gas pressures during: power - start a heating cycle. 1 Standby Mode 6 The rise in manifold pressure and corresponding drop in supply gas pressure confirms the water...
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Page 19: Air Pressure Switches
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCHES Air pressure switch technical bulletins TB-A023-06 and TB-S023-06 explain air pressure switch construction and test procedures in detail. These technical bulletins are available on the manufacturers web site or by calling the technical support phone number shown on the water heater labeling. - Page 20 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCHES (CONT) The water heater covered in this Service Manual is factory equipped with three air pressure switches. These switches are used to provide verification or prove electrically that the blower is running and that the vent and intake air pipes are not blocked or restricted.
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Page 21: Air Pressure Switch Operation
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCH OPERATION The control system monitors the “state” of the air pressure switches individually through three separate circuits (see wiring on diagram page 39). The “state” of the switch refers to whether the switch contacts are open or closed. -
Page 22: Air Pressure Switch Testing
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCH TESTING Air pressure switch testing involves three procedures: • Normal State Test • Operational State Test • Pressure Test Normal State Test Turn off power and disconnect the wires to the pressure switches. Wrap electrical tape around the wire ends to prevent shorts. - Page 23 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCH TESTING (CONT) Pressure Test The Pressure Test is necessary when the air pressure switch in question has passed the Normal State Test but failed the Operational State Test (see page 21). This test requires a digital manometer (see Tool Requirements page 3 and the images on page 23).
- Page 24 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL AIR PRESSURE SWITCH TESTING (CONT) BLOWER PROVER SWITCH PRESSURE TEST BLOCKED INTAKE SWITCH PRESSURE TEST BLOCKED EXHAUST SWITCH PRESSURE TEST Technical Literature Department 23 of 52 Ashland City, TN © 2008 Servicing should only be performed by a Qualified Service Agent...
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Page 25: Flame Sensing Test
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FLAME SENSING TEST To prove burner flame during ignition the control system monitors flame sensing current through the flame sensor. It is a DC micro amp (µA) current that flows through the flame sensor. -
Page 26: Igniter Current Test
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL IGNITER CURRENT TEST The water heater covered by this Service Manual uses a hot surface igniter (HSI). The control system CCB (page 35) powers the igniter (120 VAC) and monitors igniter current (AC amps). -
Page 27: Control System
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CONTROL SYSTEM INTRODUCTION This portion of the service manual will cover the control system. The control system includes several components: a UIM (User Interface Module), a CCB (Central Control Board), and an Overlay/Button Pad. -
Page 28: Uim
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL The UIM (User Interface Module) is the display on the front of the water heater. The UIM’s major components include a Circuit Board with LCD display and a Button Pad Overlay which contains the five user input buttons. -
Page 29: Discreet Menu - Contact Information
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL UIM (CONT) User input buttons on the UIM include an Up, a Down, and three Operational buttons. The Up and Down buttons are used to navigate through the various menus and screens displayed and to adjust or change user settings such as the Operating Set Point. - Page 30 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL UIM (CONT) Desktop Screen The Desktop screen is the default screen. If there are no active fault messages the display will return to this screen with no user input after approximately 10 minutes. The Desktop screen displays text and icons that provide operational and diagnostic information.
- Page 31 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL UIM (CONT) Table 4 - Status Icons STATUS ICON DESCRIPTION The temperature of the water in the tank has fallen and the water heater will now initialize a new heating cycle. The temperature of the water in the tank has reached the Operating Set Point.
- Page 32 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL UIM (CONT) Table 5 - Operational States (Modes) STATE DESCRIPTION The water heater is not in an active heating cycle. This usually means the temperature Standby in the tank has reached Operating Set Point and has not dropped low enough to initiate a call for heat.
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Page 33: Operating Set Point Adjustment
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL OPERATING SET POINT ADJUSTMENT When the temperature sensed by the control system at the Temperature Probe (top of the water heater) reaches the Operating Set Point the control system will end the heating cycle. A call for heat will be activated again when the tank temperature drops below the Operating Set Point minus the Differential setting plus one degree. -
Page 34: Control System Menus
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CONTROL SYSTEM MENUS Desktop: This is the default screen for the control system. If there are no active faults or warnings the display will return to this screen with no user input after approximately 10 minutes. - Page 35 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CONTROL SYSTEM MENUS (CONT) Heater Information: This menu contains historic operational and configuration information. Information/settings available: • Elapsed Time - hrs & mins - how long the water heater has been powered on •...
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Page 36: Ccb
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL The CCB circuit board is the main control. All instructions for ignition and temperature control originate from this circuit board. Diagnostic and operational messages are generated by the CCB and sent to the UIM (page 27). Most of the water heater’s components, such as the igniter, blower, gas valve, and temperature probe are directly connected to one of the CCB’s socket connectors. -
Page 37: Socket Identification
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CCB (CONT) Socket Identification All wiring connections and sockets will be identified in the following pages. The Troubleshooting section of this Service Manual will refer back to this illustration and information. - Page 38 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CCB (CONT) J1 Socket - Transformer PIN # DESCRIPTION 120 VAC hot to transformer Not used 120 VAC neutral to transformer 24 VAC out from transformer 24 VAC out from transformer J2 Socket - 120 VAC To Blower PIN # DESCRIPTION...
- Page 39 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CCB (CONT) J7 Socket - Temperature Probe/ECO (immersion probe - top of the water heater) PIN # DESCRIPTION ECO (energy cut out) 24 VAC out (red wire) Upper temperature probe (thermistor) +5.0 VDC (black wire) Upper temperature probe (thermistor) -5.0 VDC (black wire) ECO (energy cut out) 24 VAC return (red wire) J9 Port - Communication Port - Not Used...
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Page 40: Wiring Diagram
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL WIRING DIAGRAM 120 VAC 1Ø Power Supply Ground Neutral Service Notes - Polarity & Ground This water heater is polarity and ground sensitive. The control system will lock out and display a fault message (“AC Reversed”) if the power supply polarity is reversed. -
Page 41: Sequence Of Operation
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL SEQUENCE OF OPERATION Call for heat initiated Control System Declares Fault Condition - Locks Out One of the following Air Pressure Switch Test Is Performed Fault Messages Displayed: Blower Prover Switch is verified open Blocked Intake and Blocked Exhaust Switches are verified closed “Blower Prover Failure”... -
Page 42: Troubleshooting
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL TROUBLESHOOTING The control system performs exhaustive self diagnostics and displays detected fault conditions in plain english fault messages on the UIM (page 27) when there is a problem. When the control system declares a fault condition it will “lock out” and disable heating. Troubleshooting procedures for the most common error messages are covered in this manual. -
Page 43: Control System Unresponsive
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL CONTROL SYSTEM UNRESPONSIVE DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES UIM Display Is Blank • Ensure the on/off switch is on and working - replace switch if defective. On/Off is turned off • Check communication cable connections at Water heater is not plugged in UIM’s J2 Socket (page 27) and the CCB’s J16... -
Page 44: Fault Messages
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “AC Reversed” • Check incoming power supply wiring to the water heater in the junction box - ensure that the hot wire is connected to the water heater’s The control system has detected the power supply black wire and the neutral wire is connected to polarity is reversed. -
Page 45: Upper Probe Short
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Upper Probe Short” • Check all wiring between the Temperature Probe and the J7 Socket on the CCB (page 36). Repair/replace anything worn or damaged. The control system has detected less than 390 ohms from the Temperature Probe on top of the •... -
Page 46: Flame Detect Error
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Flame Detect Error” • The burner has not shut down properly. Check gas valve for 100% closure. Check for flame candling after the heating cycle has ended The control system has detected flame sensing through the Burner View Port, see page 11. -
Page 47: Blocked Inlet
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Blocked Inlet” • If the water heater has been installed as a con- ventional vent appliance - Ensure the intake air connection screen is not clogged with debris. The control system has detected open contacts at See Service Notes - Venting on page 7. -
Page 48: Blocked Exhaust Vent
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Blocked Exhaust Vent” • Check for restrictions, too many equivalent feet, or too many elbows in the vent pipe. Ensure The control system has detected open contacts at •... -
Page 49: Blower Prover Open - Blower Not Running
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Blower Prover Open” PERFORM ALL THESE TESTS WITH POWER TURNED ON AND A CALL FOR HEAT ACTIVE. (Blower Not Running) • Check for 120 VAC at the CCB’s J2 Socket The control system has detected open contacts at (page 36) pins 1 &... -
Page 50: Low Igniter Current
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Low Igniter Current” • Check all wiring between CCB’s J5 Socket (page 35) pins 1 & 2 and the hot surface igniter. Repair/replace anything worn or damaged as The control system has detected less than 2.0 AC necessary. -
Page 51: Ignition Failure
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Ignition Failure” • Visually check for burner flame through the view port on the top of the water heater (see illustra- tions on page 11) during the Ignition Verification The control system has detected less than 1.0 µA operating state (Table 5 - page 31) - the Gas (DC micro amps) through the flame sensor during... - Page 52 ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Ignition Failure” • Check for 24 VAC to the Gas Valve solenoid coil at the in-line male/female spade connectors during the Ignition Activation operating state The control system has detected less than 1.0 µA (Gas Valve icon will be visible on the UIM dis- (DC micro amps) through the flame sensor during...
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Page 53: Gas Valve Failure
ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL FAULT MESSAGES (CONT) DISPLAYED MESSAGE CHECK/REPAIR CONDITION/INDICATES “Gas Valve Failure” • Turn off power - check all wiring and connectors between the CCB’s J6 Socket (page 35) pins 2 & 15 and the Gas Valve’s solenoid coil. Repair/ The control system has not detected any current replace anything worn or damaged as neces- through the gas valve after it has been energized. - Page 54 500 Tennessee Waltz Parkway Ashland City, TN 37015...
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Questions and answers
How to adjust orange flame when heater is running too rich
An orange flame on the A.O. Smith BTX-100 heater may indicate a restricted combustion air path. To adjust or correct this issue:
1. Check the bottom base pan for obstructions or blockages.
2. Ensure the combustion air path is clear.
3. Inspect the exhaust venting and air openings for any restrictions.
If the issue persists, further inspection or servicing by a qualified technician may be required.
This answer is automatically generated