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A.O. Smith BTX 100, Service Handbook, Page: 1 / 72

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A.O. Smith BTX 100 Service Handbook Download Page 1

CommerCial / residential gas water heater

service handbook

PRINTED IN THE U.S.A. 0410 

318556-000

serviCing should only be performed by a Qualified serviCe agent

500 Tennessee Waltz Parkway

Ashland City, TN 37015

for models:

btX 100, gdhe 50

series 120 & 121

installation Considerations -  pre serviCe

CheCKs - water heater ConstruCtion -

operation & serviCe - troubleshooting

Summary of Contents for BTX 100

Page 1: ...0410 318556 000 Servicing should only be performed by a Qualified Service Agent 500 Tennessee Waltz Parkway Ashland City TN 37015 FOR MODELS BTX 100 GDHE 50 SERIES 120 121 INSTALLATION CONSIDERATIONS...

Page 2: ......

Page 3: ...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 Replaceme...

Page 4: ...ions given in this manual do not attempt to perform any procedures outlined in this manual Service Reminder When performing any troubleshooting step outlined in this manual always consider the wiring...

Page 5: ...ter discharged from the valve due to excessive pressure build up This condition is not covered under the limited warranty The Temperature Pressure Relief Valve is not intended for the constant relief...

Page 6: ...ments The the intake air and or vent pipe for the water heaters covered in this manual can be installed using 2 inch or 3 inch pipe depending on the overall equivalent length of each pipe Equivalent l...

Page 7: ...switch sensing tube If water does enter the Blocked Intake Air switch sensing tube it will damage the switch and cause Blocked Air Intake fault conditions and Control System lock outs Ensure this hose...

Page 8: ...wire from the power supply must connect to the green wire inside the 120 VAC junction box on the water heater A Reversed Polarity condition occurs when the hot and neutral wires are connected in reve...

Page 9: ...stem lock outs 6 Ensure there is a water trap formed in the condensate drain tube line connected to the exhaust elbow on the water heater and that the condensate drain is flowing freely Condensate dra...

Page 10: ...NECTION CONDENSATE DRAIN CONNECTION BLOCKED EXHAUST SWITCH SENSING TUBE HEATING LOOP SUPPLY LINE CONNECTION 3 4 INCH NPT 2 INCH PVC INTAKE AIR CONNECTION TOP COVER ON OFF SWITCH UIM user interface mod...

Page 11: ...2 INCH PVC INTAKE AIR CONNECTION 2 INCH PVC VENT CONNECTION JUNCTION BOX 120 VAC POWER SUPPLY CONNECTIONS SECOND ANODE ROD Figure 4 Combustion Blower Burner Assembly COMBUSTION BLOWER EXPLODED VIEW GA...

Page 12: ...burning gases are forced through the heat exchanger under pressure and exit through the exhaust vent connection located at the bottom of the water heater Starting at the top air and fuel gas are draw...

Page 13: ...ol System LCD during the Igniter Warm Up operating state see Table 5 on page 47 Service Note The 5 pin PWM signal plug MUST remain plugged in to the 5 pin socket on the blower assembly at all times Di...

Page 14: ...ner Assembly removed from the water heater with key components identified See the exploded view of the Combustion Blower Burner Assembly on page 9 also BURNER ADAPTER WIRING HARNESS IGNITER FLAME SENS...

Page 15: ...N PLACE BURNER ADAPTER WIRING HARNESS IGNITER FLAME SENSOR Figure 10 BURNER SIGHT GLASS BURNER ADAPTER WIRING HARNESS IGNITER FLAME SENSOR BLOWER DISCHARGE ORIFICE BLOWER FLANGE WITH ORIFICE REMOVED F...

Page 16: ...parts Have the complete Model Series and Serial number located on the water heater s rating label for the water heater being serviced on hand before calling Do not place any screws studs nuts parts or...

Page 17: ...llen key wrench remove the four hex head machine screws that hold the Combustion Blower to the Burner Adapter see Figure 15 on page 16 13 Lift the Combustion Blower up and off of the Burner Adapter se...

Page 18: ...y straight up and out of the water heater s heat exchanger opening see Figure 17 on page 17 8 Inspect the Flame Sensor and its ceramic insulator for cracks and wear Replace the Flame Sensor if it show...

Page 19: ...lso See Figure 5 on page 9 19 Do not overtighten the 5 16 inch hex head machine screws holding the Burner to the Burner Adapter or the 1 2 inch nuts that hold the Burner Adapter to the Heat Exchanger...

Page 20: ...ols Required on page 2 IGNITER BURNER FLAME BURNER MUST BE GROUNDED CERAMIC INSULATOR FLAME SENSOR METAL CONDUCTOR CONTROL SYSTEM APPLIES AC VOLTAGE TO FLAME SENSOR AC VOLTAGE FLOWS FROM THE FLAME SEN...

Page 21: ...S FROM CCB WIRE FROM FLAME SENSOR WIRE FROM FLAME SENSOR Figure 19 Service Notes The Flame Sensor wire behind the CCB is one of three wires in a harness that also serves the Igniter Ensure you have id...

Page 22: ...o longer working at all IE if the measured resistance is an open circuit infinite ohms the Igniter must be replaced However the resistance of the Igniter varies with temperature and with the test mete...

Page 23: ...ing the Igniter Warm Up operating state Ensure the wiring and connections between the J5 Socket on the CCB and the Burner Adapter are not broken pinched or disconnected Ensure there is approximately 1...

Page 24: ...es A pressure drop occurs at this point and creates a negative pressure in the cavity between the cone shaped restrictor and the Venturi housing This negative pressure pulls gas from the outlet of the...

Page 25: ...d to the 24 Volt Gas Valve at pins 2 and 15 of the J6 Plug on the CCB see CCB Cover Removal And Replacement on page 40 and CCB Circuit Board Layout on page 41 Using an AC volt meter insert the two tes...

Page 26: ...crew for the wiring harness plug on the valve and disconnect the plug see Figure 23 on page 23 4 Turn off the supply gas to the water heater at the main gas shutoff valve serving the water heater 5 Di...

Page 27: ...48 This pressure will be considerably lower 5 00 W C to 7 50 W C during the Pre Purge and Post Purge operating states when the Combustion Blower is running at high speed and the 24 Volt Gas Valve is...

Page 28: ...11 Record the manifold offset pressure when the Combustion Blower starts and ramps up to high speed during the Pre Purge operating state should be in a deep vacuum 5 00 W C to 7 50 W C 12 Return the...

Page 29: ...ghtly Follow the procedure to connect two digital manometers to the 24 Volt Gas Valve in the Gas Pressure Test on page 26 Observe the pressure changes during the three operating states listed in Figur...

Page 30: ...is sealed The other chamber is vented to the atmosphere which allows the diaphragm to move up and down There is linkage that attaches the switch contacts to the diaphragm so that when the diaphragm m...

Page 31: ...the Blower Prover switch contacts have closed see the Sequence Of Operation Flow Chart on page 55 The Blocked Intake Air and Blocked Exhaust switch contacts must remain closed at all times If the Blo...

Page 32: ...num connecting tube mounted on the side of the water heater between the Blocked Exhaust switch at the top and the exhaust elbow at the bottom Two short pieces of plastic sensing tube are used at eithe...

Page 33: ...ater heater at the water heater s on off switch 3 Disconnect both wires at each pressure switch 4 Using an ohm meter set for continuity testing check for continuity between the two wiring terminals at...

Page 34: ...ort these switches have passed the test Failed Results If the Blower Prover switch contacts do not close during this test the Pressure Test During Operation below must be performed to determine if the...

Page 35: ...l number located on the water heater s rating label for the water heater being serviced on hand before calling Blocked Intake Air Note these are negative pressures in a vacuum If the pressure reading...

Page 36: ...34 Servicing should only be performed by a Qualified Service Agent BLOWER PROVER SWITCH PRESSURE TEST BLOCKED INTAKE AIR SWITCH PRESSURE TEST BLOCKED EXHAUST SWITCH PRESSURE TEST Figure 34...

Page 37: ...ble 4 on page 36 The Control System interprets changes in the temperature sensor resistance as changes in water temperature and uses this data to activate and deactivate heating cycles and displays th...

Page 38: ...ed wires the ECO switch has reset properly If the Control System continues to lock out displaying Energy Cut Out ECO on the LCD with continuity through the ECO present call the toll free support phone...

Page 39: ...ergized by the Control System See Features And Components on page 8 for the location of these components Components The main components of the Control System are a UIM User Interface Module and a CCB...

Page 40: ...inserted into the Ribbon Cable plug whenever removing or installing the UIM or the Button Pad Overlay It is possible to connect the Ribbon Cable Plug incorrectly It can be plugged in upside down with...

Page 41: ...f the water heater s components such as the Igniter Combustion Blower 24 Volt Gas Valve and Temperature Probe are directly connected to one of the CCB s socket connectors If the CCB fails the replacem...

Page 42: ...power to the water heater is turned off 2 Remove the 4 screws that hold the top cover in place 3 Remove the 2 CCB cover screws from the CCB 4 Swing the cover away from the enclosure from left side and...

Page 43: ...switch array there are numbers 1 4 On the other side of the dipswitch is the word OPEN The dipswitches are rocker type switches if one side of the rocker is down the other side will be up Pressing a r...

Page 44: ...3 120 VAC neutral J4 Male Spade Connector Flame Sensor J5 Socket Igniter 120 VAC HSI hot surface igniter Pin Description 1 120 VAC hot 2 120 VAC neutral J6 Socket 24 Volt Gas Valve Pressure Switches E...

Page 45: ...out 24 VAC return red wire J9 Port Communication Port Not Used J10 Socket Not Used J11 Port Communication Port Not Used J13 Socket Blower Speed Control Pin Description 1 Not used 2 Not used 3 To 5 pin...

Page 46: ...USER INTERFACE MODULE I U 2 15 4 14 5 10 6 7 8 11 L N 1 4 5 3 WHITE GREEN 7 WHITE BLUE 8 WHITE BROWN 2 RED GREEN WHITE N O I T C N U J X O B N E E R G N E E R G ENABLE DISABLE CIRCUIT JUMPER WIRE BET...

Page 47: ...eir are operational problems see Service Contact Information on page 53 Animated Status Icons The Control System displays animated Status Icons on the LCD that indicate when each critical step in the...

Page 48: ...s the default screen The Control System will return to the Desktop Screen when there are no active Fault or Alert conditions or when there has been no user input for several minutes Manufacturer and w...

Page 49: ...The check mark icon is visual confirmation of contact closure The Igniter is being energized The Igniter has been energized and the Control System has sensed the required minimum Igniter current The...

Page 50: ...cycled off and on to reset the Control System Note Cycling power will not reset the Control System if the condition that caused the Fault has not been corrected Control System Menus From the Desktop S...

Page 51: ...own Buttons to view all Control System menus from the Main Menu With Temperatures menu selected highlighted in black in the Main Menu screen press the Operational Button under SELECT to enter the Temp...

Page 52: ...Status displays the current Operating State see Table 6 on page 48 for a description of the various operational states ECO Contact Blocked Inlet PS Blocked Outlet PS Blower Prover PS displays the cur...

Page 53: ...djustable operational information Elapsed Time Total accumulated time the Control System water heater has been energized Burner On Time Total accumulated time the Control System has been in the heatin...

Page 54: ...erational Button under VIEW to view details for each Fault or Alert message stored Note fault history memory is cleared after 30 days 1 Blocked Air Intake A7 51 mins ago 2 Blocked Exhaust A8 54 mins a...

Page 55: ...ough this menu item Show Contact Information Yes Change Contact Name Change Contact Phone Current Contact Info 000 000 0000 Access Code UPDATE CANCEL Service Contact Information Using the UP and DOWN...

Page 56: ...contacts are confirmed closed the Control System energizes the Igniter for the Igniter Warm Up operating state See Operating States on page 48 8 The Control System monitors Igniter current and must se...

Page 57: ...lt Gas Valve is energized gas flows to Burner Does Control System sense minimum flame sensing of 1 0 A DC micro amps through Flame Sensor Control System Locks Out Displays Fault Msg Combustion Blower...

Page 58: ...the contacts for the Blower Prover Blocked Intake Air and Blocked Exhaust switches This information is displayed in real time Use this menu when troubleshooting to quickly and accurately diagnose oper...

Page 59: ...e UIM User Interface Module on page 37 and the CCB s J16 Socket page 41 Secure power and install a new comm cable standard Cat 5 network cable Closely inspect communication ports on CCB and UIM for da...

Page 60: ...res outlined here Temp Probe Open The Control System has detected more than 56 000 ohms from the Temperature Sensor inside the Temperature Probe CHANGE BACK ADVANCED Temp Probe Open Fault occurred 2 m...

Page 61: ...ed Adjust gap between the Flame Sensor and the Burner Call the toll free support phone number on the back cover of this manual for further assistance if the problem has not been corrected after perfor...

Page 62: ...further assistance Do not leave the water heater in operation under any circumstances If recorded temperature from above is below 180 cycle power to reset the Control System Watch the water heater th...

Page 63: ...ng Review venting installation section of the Instruction Manual that came with the water heater see Table 1 on page 4 in this manual Ensure the vent intake air piping has been installed within manufa...

Page 64: ...ll allow water condensate to collect and block the vent piping Check all wiring between the Blocked Exhaust switch and the CCB s J6 Socket page 41 pins 5 10 Perform close visual inspection of the pins...

Page 65: ...tion of the pins inside the plug and socket at the Combustion Blower s high voltage 3 Pin Socket ensure the plugs and sockets are mating properly and providing good contact Disconnect the plug at the...

Page 66: ...ecessary Perform close visual inspection of the pins inside the CCB J5 plug and socket ensure plugs and sockets are mating properly and providing good contact Repair replace anything worn or damaged a...

Page 67: ...ht Glass The animated Gas Valve Status Icon appears on the Desktop Screen during the Ignition Verification operating state See Desktop Screen on page 46 and Status Icons on page 47 Ensure the Burner i...

Page 68: ...lean the Flame Sensor with fine steel wool check for signs of excessive wear bent damage cracks in the insulator replace Flame Sensor if worn or damaged Check adjust the gap between the Flame Sensor a...

Page 69: ...NOTES...

Page 70: ...NOTES...

Page 71: ......

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...

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