A.O. Smith BTX 100 Service Handbook

Series 120 & 121 commercial / residential gas water heater

Hide thumbs Also See for BTX 100:

Instruction manual (60 pages)

Instruction manual (60 pages)

Service handbook (54 pages)

Table Of Contents

Table of Contents

Quick Links

Summary of Contents for A.O. Smith BTX 100

Page 1 CommerCial / residential gas water heater for models: btX 100, gdhe 50 series 120 & 121 installation Considerations - pre serviCe 500 Tennessee Waltz Parkway CheCKs - water heater ConstruCtion - Ashland City, TN 37015 operation & serviCe - troubleshooting serviCing should only be performed by a Qualified serviCe agent PRINTED IN THE U.S.A.
Page 3: Table Of Contents
table of Contents TAblE Of CONTENTS ................1 Control System Hardware ............37 INTRODUCTION ..................2 uIM (user Interface Module) ..........37 Qualifications ..................2 CCB (Central Control Board) ..........39 Service Warning ................2 CCB Cover Removal And Replacement ......40 Service Reminder ................
Page 4: Introduction
introduCtion This Service Manual covers the water heater Model and Series numbers listed on the front cover only. The instructions and illustrations contained in this manual will provide you with troubleshooting procedures to verify proper operation and diagnose and repair common service problems. QualifiCations Qualified installer or serviCe agenCy Installation and service of this water heater requires ability equivalent to that of a Qualified Agency (as defined...
Page 5: Installation Considerations
installation Considerations This section of the Service Manual covers some of the critical installation requirements that, when overlooked, often result in operational problems, down time and needless parts replacement. Costs to correct installation errors are not covered under the limited warranty. Ensure all installation requirements and instructions contained in the Instruction Manual that came with the water heater have been followed prior to performing any service procedures.
Page 6: Venting
venting This section of the Service Manual is not a complete venting installation instruction. Refer to the Instruction Manual that came with the water heater; ensure the venting has been installed per all Instruction Manual requirements. Costs to correct installation errors are not covered under the limited warranty. general venting information The water heaters covered in this manual are operationally equivalent to Category IV appliances and may be installed in either a Power Vent or direct Vent configuration.
Page 7: Intake Air Connection
faCtory supplied/installed fittings Factory supplied vent and intake air terminations and factory installed fittings on the water heater are not factored in to the vent and intake air pipe equivalent feet calculations. The intake air connection fitting and exhaust elbow (vent connection) are factory installed fittings, see Figure 1 below and Figure 3 on page 8. intaKe air ConneCtion The intake air connection has a screen and a hose barb installed at the factory, see Figure 1 below.
Page 8: Electrical Requirements
eleCtriCal reQuirements The water heaters covered in this manual require a 120 VAC (Volts Alternating Current) 1Ø (Single Phase) power supply. The maximum AC amperage is approximately 5.2 FLA (full load amps) during the Igniter Warm up operating state. Residential models are factory equipped with a 3 prong appliance cord that plugs into a standard 120 VAC wall outlet.
Page 9: Installation Check List
installation CheCK list The list below represents some of the most critical installation requirements that, when overlooked, often result in operational problems, down time and needless parts replacement. Before performing any troubleshooting procedures use the list below to check for installation errors. Costs to correct installation errors are not covered under the limited warranty.
Page 10: Features And Components
features and Components front & baCK views FRONT VIEW BACK VIEW TOP COVER 2 INCH PVC INTAKE AIR CONNECTION ON / OFF SWITCH HEATING LOOP SUPPLY LINE (user interface module) CONNECTION 3/4 INCH NPT CONTROL INTERFACE COVER. TEMPERATURE TEMPERATURE PROBE - LOCATED PRESSURE BEHIND CONTROL RELIEF VALVE...
Page 11: Top View
top view 1/2 INCH BLOCKED SUPPLY GAS INTAKE AIR 2 INCH PVC SECOND CONNECTION SWITCH INTAKE AIR ANODE ROD CONNECTION COMBUSTION 2 INCH PVC BLOWER VENT CONNECTION JUNCTION BOX - 120 VAC BLOCKED POWER SUPPLY EXHAUST CONNECTIONS SWITCH BLOWER PROVER 3/4 INCH NPT SWITCH WATER INLET...
Page 12: Operation And Service
OPERATION AND SERvICE how it worKs This section of the manual will cover operation, common service procedures and water heater construction. The water heater covered in this manual has a helical shaped coil heat exchanger that is submerged in the storage tank. These water heaters use a top mounted down fired radial design Burner. This is a forced draft burner;...
Page 13: Combustion Blower
Combustion blower The Combustion Blower is an assembly that includes the blower housing, blower motor and an electronic speed control. The Combustion Blower is controlled by the CCB (Central Control Board), see Control System Hardware on page 37. The CCB sends 120 VAC from the J2 socket on the CCB circuit board to a 3 pin wiring socket on the blower assembly, see CCB Circuit Board Layout on page 41 and Figure 7 below.
Page 14: Burner Assembly
burner assembly The Burner is a radial design burner with a steel fiber jacket on the outer surface and is part of a larger Burner Assembly. Figure 8 and Figure 9 below show side views of the complete Burner Assembly removed from the water heater with key components identified.
Page 15 BURNER ADAPTER WIRING HARNESS IGNITER/FLAME SENSOR BURNER GROUND WIRE BURNER BLOWER FLANGE WITH BLOWER ADAPTER DISCHARGE ORIFICE IN PLACE Figure 10 BURNER SIGHT GLASS BLOWER DISCHARGE ORIFICE BURNER ADAPTER WIRING HARNESS IGNITER/FLAME SENSOR BLOWER FLANGE WITH ORIFICE REMOVED Figure 11 BLOWER BURNER ADAPTER BLOWER...
Page 16: Combustion Blower And Burner Removal
Combustion blower and burner removal The Combustion Blower and Burner Assembly must be removed to inspect the Burner and to service the Flame Sensor and Igniter. This section will provide instructions on how to remove and inspect these components. Service Notes: •...
Page 17 6. disconnect the 24 Volt power wires to the 24 Volt Gas Valve at the two spade connectors in the wiring harness to the valve, see Figure 14 below. 7. disconnect the Blower Prover switch sensing tube from the Combustion Blower outlet sensing port, see Figure 14 below.
Page 18 Figure 15 burner assembly removal 1. Follow the instructions to remove the Combustion Blower beginning on page 14. 2. Remove the Blower discharge orifice from the top of the Burner Adapter. 3. unplug the Burner Adapter wiring harness; three male/female spade connections for the Igniter and Flame Sensor behind the CCB enclosure, see Figure 10 on page 13.
Page 19 burner assembly installation 17. To re-install the Burner Assembly follow the steps for removal in reverse order. 18. Install a new white fiber gasket between the Burner Adapter and the Heat Exchanger Flange on top of the water heater. Install a new white fiber gasket between the Burner and the Burner Adapter also. See Figure 5 on page 9.
Page 20: Flame Sensor
flame sensor Ignition of the Burner is controlled electronically. The principle of operation for electronic ignition relies on flame sensing current to prove the fuel gas flowing to the Burner has been ignited and is burning safely. Flame sensing requires correct power supply polarity and an adequate earth ground to the water heater's Burner, see Electrical Requirements and the Power Supply Test on page 6.
Page 21: Flame Sensing Current Test
flame sensing Current test during the heating cycle the flame sensing current is normally between 8.0 μA and 12.0 μA with a clean Flame Sensor. over time the Flame Sensor will accumulate corrosion (rust) and this will reduce flame sensing current.
Page 22: Igniter
igniter The water heaters covered by this manual use a hot surface igniter (HSI). The Igniter is made of a ceramic composite material, see Figure 20 below. The Control System powers the Igniter (120 VAC) from the J5 Socket on the CCB. The Control System monitors amperage through the Igniter to ensure it is hot enough to ignite the fuel gas flowing to the Burner during ignition.
Page 23 IGNITER CURRENT TEST AT J5 SOCKET ON CCB IGNITER CURRENT TEST BEHIND CCB ENCLOSURE Figure 21 Service Notes: • The animated lighting bolt Status Icon is visible on the LCd desktop Screen during the Igniter warm up operating state. See desktop Screen on page 46 and Status Icons on page 47. •...
Page 24: Venturi
venturi A Venturi is mounted on the inlet of the Combustion Blower. All combustion air flows through the Venturi. The outlet of the 24 Volt Gas Valve connects directly to the side of the Venturi. Fuel gas flows from the outlet of the 24 Volt Gas Valve into the side of the Venturi directly.
Page 25: Gas Valve
gas valve The 24 Volt Gas Valve on these water heaters is dC voltage valve. The CCB sends 24 VAC to the valve and the AC voltage is rectified into a dC voltage by electronics contained inside the plug end of the 24 Volt Gas Valve wiring harness, see Figure 23 below.
Page 26: Gas Valve Removal
gas valve removal The outlet of the 24 Volt Gas Valve is connected by flange directly to the side of the Venturi and is secured by three - 5/32” hex head screws. A gas orifice with gasket is fitted into the gas valve’s outlet flange, see Figure 25 and Figure 26 below.
Page 27: Gas Pressure
gas pressure 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 (3,078 meters). For higher elevations call the toll free support phone number shown on the back cover of this manual for technical assistance.
Page 28: Gas Pressure Test
gas pressure test 1. If the water heater is in a heating cycle lower the operating Set Point to end the cycle, see Temperatures on page 49. 2. Turn off power to the water heater at the water heater's on/off switch. 3.
Page 29: Gas Flow Test
gas flow test The following illustrations show the approximate pressures for the manifold offset and supply gas for the Standby, Pre-Purge and Heating operating states during a normal heating sequence. notice how the manifold offset pressure starts at 0" W.C. in the Standby operating state, falls to a deep vacuum during the Pre-Purge state and then rises to a slight positive pressure when the 24 Volt Gas Valve is energized during the Heating state.
Page 30: Pressure Switches
pressure switChes The water heaters covered in this manual are factory equipped with three pressure switches. Figure 4 on page 9 shows the location of the three pressures switches on top of the water heater. This section of the manual covers pressure switch construction, operation and the test procedures used to diagnose operational problems associated with pressure switches.
Page 31: Control System Monitoring
Control system monitoring The Control System monitors the “state” of the pressure switch contacts individually through three separate circuits, see Wiring diagram on page 44. The state of the switch refers to whether the switch contacts are open or closed, see Construction & operation on page 28. At the beginning of a heating sequence, before the Combustion Blower is energized, the Control System enters the Input Verification operating state, see operating States on page 48.
Page 32 Sensing Tubes The three pressure switches monitor pressure through plastic sensing tubes from three different sensing ports on the water heater, see Figure 32 below. The Blower Prover switch monitors pressure from the Combustion Blower's outlet, see Figure 14 on page 15. The Blocked Intake Air switch monitors pressure from the Combustion Blower’s intake air connection fitting, see Figure 1 on page 5.
Page 33: Pressure Switch Tests
pressure switCh tests Complete pressure switch testing involves three procedures: • Continuity Test during Standby below. • Continuity Test during operation on page 32. • Pressure Test during operation on page 32. Continuity test during standby This test is performed while the Combustion Blower is not running with the water heater turned off. This is a "normal state"...
Page 34: Continuity Test During Operation
Continuity test during operation This test is performed while the Combustion Blower is running at high speed during the Pre-Purge operating state. The test is performed on all three pressure switches. disconnect the two wires to each pressure switch - one at a time, check continuity and then reconnect the wires to that switch before testing the next switch. 1.
Page 35 table 3 blower prover blocked intake air Blocked Exhaust †Activation Pressure +0.75" W.C. -2.00" W.C. +2.00" W.C. Tolerance ± 0.05" W.C. ± 0.05" W.C. ± 0.05" W.C. †Though it is uncommon, pressure switch specifications can be changed by the manufacturer. These activation pressures are current as of the (month/year - expressed as MM/yy) date code printed on the front cover of this manual in the lower left corner.
Page 36: Blocked Exhaust Switch
BLOWER PROVER SWITCH PRESSURE TEST BLOCKED INTAKE AIR SWITCH PRESSURE TEST BLOCKED EXHAUST SWITCH PRESSURE TEST Figure 34 Servicing should only be performed by a Qualified Service Agent...
Page 37: Temperature Probe
temperature probe This section of the manual provides information on the Temperature Probe, see Figure 3 on page 8 for location. The Temperature Probe contains the ECo (energy cut out) and a Temperature Sensor. The Temperature Probe connects to the J7 Socket on the CCB, see CCB Circuit Board Layout on page 41 and CCB Connection Identification on page 42.
Page 38: Eco Continuity Test
TABlE 4 water temperature temperature sensor resistanCe in ohms Celsius fahrenheit 3° 40° 26,435 21° 70° 11,974 38° 100° 5,862 49° 120° 3,780 55° 130° 3,066 60° 140° 2,503 71° 160° 1,698 82° 180° 1,177 eCo Continuity test 1. Turn off power to the water heater at the water heater's on/off switch. 2.
Page 39: Control System Hardware
Control system hardware This section of the manual will provide information on Control System hardware , operation and service procedures. See Control System operation on page 45 for information on Control System features, navigation, menus, and user settings. The water heaters covered in this manual are equipped with an electronic Control System that regulates water temperature inside the storage tank.
Page 40 uim ribbon Cable ConneCtion Service Notes: The Ribbon Cable that connects the Button Pad overlay to the uIM Circuit Board must be plugged in exactly as shown in Figure 36 on page 37. The metal crimp connections in the Ribbon Cable plug must be facing away from the uIM circuit board.
Page 41: Ccb (Central Control Board)
CCB (CENTRAl CoNTRol BoARD) The CCB is a printed circuit board mounted inside a protective plastic enclosure, see Figure 38 and Figure 39 below. The CCB circuit board is the main control. All instructions for ignition and temperature control originate from this circuit board.
Page 42: Ccb Cover Removal And Replacement
CCb Cover removal and replaCement The cover on the CCB enclosure must be removed for various service procedures outlined in this manual. Refer to the instructions on page 40 when removing and replacing the CCB cover. Wiring to and from the CCB and other water heater components enters the CCB enclosure on the left side. Strain relief for the wiring is provided between the enclosure's front cover and the internal transformer cover.
Page 43: Ccb Circuit Board Layout
CCb CirCuit board layout CCB (CENTRAL CONTROL BOARD) 1 Retry Retries Input Type Tstat Vent Spare Spare S1 DIPSWITCH S1 DIPSWITCH DETAIL 1 Retry Retries Input Type Tstat Vent Spare Spare Dipswitch Operation: Along one side of the dipswitch array there are numbers, 1-4. On the other side of the dipswitch is the word “OPEN.”...
Page 44: Ccb Connection Identification
CCb ConneCtion identifiCation 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 Combustion Blower pin # desCription 120 VAC hot to Combustion Blower 3 pin socket, see Figure 7 on page 11...
Page 45 CCB CoNNECTIoN IDENTIFICATIoN (CoNT) J7 Socket - Temperature Probe/ECo (immersion probe) pin # desCription ECo (energy cut out) 24 VAC out (red wire) Temperature Sensor (thermistor) +5.0 VdC (black wire) Temperature Sensor (thermistor) -5.0 VdC (black wire) ECo (energy cut out) 24 VAC return (red wire) J9 Port - Communication Port - Not Used J10 Socket - Not Used J11 Port - Communication Port - Not Used...
Page 46: Wiring Diagram
wiring diagram 24 VOLT BLOCKED BLOCKED BLOWER GAS VALVE INTAKE AIR PROVER EXHAUST ENABLE/DISABLE CIRCUIT JUMPER WIRE BETWEEN PINS 8 AND 11 ON J6 PLUG HOT SURFACE IGNITER 1 BLACK 2 WHITE FLAME SENSOR 1 RED (ECO) 2 BLACK 3 BLACK TEMPERATURE PROBE 4 RED (ECO) PWM (Pulse Width Modulation)
Page 47: Control System Operation
Control system operation overview This section of the manual provides instructions and information on Control System features, navigation, menus, and user settings. See Control System Hardware on page 37 for information concerning the Control System hardware and components. The water heaters covered in this manual are equipped with an electronic Control System that controls all water heater functions.
Page 48: Commercial And Residential Models
CommerCial and residential models The water heaters covered by this manual are produced for commercial and residential use. The Control System is programmed differently for commercial and residential models. There are two differences in Control System operation between the residential and commercial products: •...
Page 49: Status Icons
status iCons The Status Icons are displayed on the desktop Screen and convey operational and diagnostic information. The icons are described in the table below. table 5 icon Description Water temperature in the tank has fallen. Shaded area of the animated thermometer icon will rise and fall in response to water temperature in the storage tank as sensed from the Temperature Probe(s).
Page 50: Operating States
operating states The current operating state of the water heater is displayed on the desktop Screen as the "Status." The common operational states are described in the table below. table 6 state Description Standby The water heater is not in an active heating cycle. IE: the Tank Temperature is at or above the operating Set Point. Input Verification The Control System is conducting a diagnostic check at the beginning of a heating cycle.
Page 51: Temperatures
temperatures operating Set Point And Differential Adjustment The operating Set Point is adjustable from 90°F (42°C) to 180°F (82°C) for commercial and 160°F (71°C) on residential models. The factory setting is 120°F (49°C). The differential is adjustable from 2° to 20°. The factory setting is 8°.
Page 52: Heater Status
temperatures menu desCription/aCtion display • Tank Temperature - non adjustable - Control System sensed temperature from the Temperature Probe. Temperatures • Tank Probe offset - adjustable user setting, range -5° to Operating Set Point 140°F +5° (factory setting 0°). Differential 8°F The Tank Probe offset is used to calibrate Control System Tank Temperature...
Page 53: Display Settings
display settings desCription/aCtion display Select display Settings from the Main Menu and press the Display Settings operational Button under "SELECT" to enter this menu. This Temperature Units °F menu contains adjustable display options for viewing information on the LCd screen. use the up & down Buttons to navigate the Backlight Delay menu.
Page 54: Current Fault
Current fault desCription/aCtion display Select Current Fault from the Main Menu and press the operational Button under "SELECT" to enter this menu. This Blocked Exhaust menu contains non adjustable operational information. use the Fault occurred 2 mins ago up & down Buttons to navigate the menu. The exhaust is blocked or This menu contains the current Fault or Alert error message.
Page 55: Service Contact Information
serviCe ContaCt information There is a discrete menu that Installing contractors and/or service agents can access to enter contact information for their customers. This contact information will be displayed with all Fault and Alert messages. desCription/aCtion display From the desktop Screen press and hold down the middle Service Contact Information (unmarked) operational Button for 30 seconds and then release Show Contact Information...
Page 56: Sequence Of Operation
seQuenCe of operation Read the Sequence of operation below before attempting to diagnose or repair any operational problems. Refer to the Features And Components on page 8 for the location of various water heater components described below. See the Sequence of operation Flow Chart on page 55 also. 1.
Page 57: Sequence Of Operation Flow Chart
seQuenCe of operation flow Chart If tank temperature drops below Operating Set Point minus Differential setting a heating cycle is activated Control System performs diagnostic system check Control System Locks Out Normal State of all pressure switches and ECO are checked Blower Prover pressure is switch verified open Displays Fault Msg All other pressure switches and ECO are verified closed...
Page 58: Troubleshooting
troubleshooting The Control System performs exhaustive self diagnostics and displays detected fault conditions in plain English fault messages on the LCd 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 fault conditions are covered in this manual.
Page 59: Control System Unresponsive
Control system unresponsive displayed message/Condition/indiCates possible Causes - CheCK/repair UIM (lCD) Is Blank • Ensure the water heater's on/off switch is in the "on" position and is working properly - replace switch if The LCd on the uIM is not showing any data. The water defective.
Page 60: Fault Messages
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair AC Reversed • Check the 120 VAC wall outlet (if applicable) supplying power to the water heater for correct The Control System has detected the power supply polarity and ground using a AC volt meter or a plug in polarity is reversed.
Page 61: Flame Sensor Short
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair Flame Sensor Short • Check all wiring and plugs between the J4 spade connector on the CCB (page 41) and the Burner The Control System has detected the Flame Sensor is Adapter wiring harness behind the CCB enclosure. grounded.
Page 62: Energy Cut Out (Eco)
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair Energy Cut out (ECo) • Be extremely careful - record temperature from a nearby hot water fixture. The Control System has detected water temperature in • If recorded temperature is above 180°F - shut off the water heater storage tank above 201°F (94°C).
Page 63: Blocked Air Intake
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair blocked air intake • If the water heater has been installed as a conventional vent appliance - Ensure screen inside The Control System has detected the Blocked Intake Air the intake air connection fitting is not clogged with switch has open contacts - restricted combustion air intake debris.
Page 64: Blocked Exhaust
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair Blocked Exhaust • Check the condensate drain on the water heater's Exhaust Elbow, see Figure 3 on page 8 for location. The control system has detected the Blocked Exhaust Water build up in the Exhaust Elbow will restrict the switch has open contacts - restricted/blocked vent piping, venting system and cause this failure.
Page 65: Blower Prover Open
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair blower prover open perform all these tests with power turned on and a Call for heat aCtive. (Combustion Blower not Running) • Check for 120 VAC at the CCB’s J2 Socket (page 41) The Control System has detected the Blower Prover pins 1 &...
Page 66: Low Igniter Current
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair low Igniter Current • Check all wiring between CCB’s J5 Socket (page 41) pins 1 & 2 and the Igniter. Repair/replace anything The Control System has detected less than 0.5 AC amps worn or damaged as necessary.
Page 67: Ignition Failure
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair Ignition Failure • Ensure the main gas shut off valve is open. The Control System has detected less than 1.0 μA (dC • Ensure there is adequate air for combustion & micro amps) through the flame sensor during the Ignition ventilation.
Page 68: Communication Failure
fault messages displayed message/Condition/indiCates possible Causes - CheCK/repair Ignition Failure • Check for flame sensing current during the Ignition Verification operating state. Perform the Flame The Control System has detected less than 1.0 μA (dC Sensing Current Test on page 19. micro amps) through the flame sensor during the Ignition Verification operating state on three consecutive trials for •...
Page 69 notes...
Page 70 notes...
Page 72 500 Tennessee Waltz Parkway, Ashland City, TN 37015 Technical Support: 800-527-1953 • Parts: 800-433-2545 • Fax: 800-644-9306 www.hotwater.com...

This manual is also suitable for:

Gdhe 50

A.O. Smith BTX 100 Service Handbook

Quick Links

Related Manuals for A.O. Smith BTX 100

Summary of Contents for A.O. Smith BTX 100

This manual is also suitable for:

Table of Contents