A.O. Smith BTH 120 Service Handbook Download Page 47

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Servicing should only be performed by a Qualified Service Technician

GAS ORIFICE - BTH 300 THRU 500 MODELS

Refer to Orifice Chart below for correct gas orifice size. BTH 120 thru 250 Models and all Natural gas

models do not use a gas orifice.

ORIFICE CHART - BTH 300 THRU 500 MODELS

Model/Series

300

200/201

400

200/201

500

200/201

Natural

N/A

Propane (LP)

0.344"

Gas Control With Orifice Propane (LP)

Gas Control Without Orifice Natural Gas

w/LP Gas Orifice

Without Orifice

BTH 300 - 500 MODELS

Summary of Contents for BTH 120

Page 1: ...U S A 0914 329297 000 500 Tennessee Waltz Parkway Ashland City TN 37015 FOR MODELS BTH 120 THRU 500 SERIES 200 201 INSTALLATION CONSIDERATIONS PRE SERVICE CHECKS CONSTRUCTION OPERATION SERVICE TROUBLE...

Page 2: ...rol 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 Temperatur...

Page 3: ...o not attempt to perform any of the procedures described in this service handbook If you do not understand the instructions given in this service handbook do not attempt to perform any procedures outl...

Page 4: ...ief Valve operation water 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 fo...

Page 5: ...er Gasket Blower Adapter Burner Gasket Burner Ignition Cable Sight Glass Sight Glass Gasket Burner Plate Burner Plate Gasket 150 250 Models Only SS Heat Shield 150 250 Models Only Flue Ring Gasket Ign...

Page 6: ...bly Exhaust Condensate Elbow Ignition Control Junction Box Assembly UIM Label Color Green Label Color Blue Label Color Red Water Outlet 1 1 2 NPT TOP VIEW BTH 300 500 MODELS Water Outlet 1 1 2 NPT CCB...

Page 7: ...ated Blower Prover switch contacts confirmed closed by control system Spark Ignition Control is energized 24 Volt Gas Valve is energized gas flows to Main Burner Is flame sensed at the Main Burner con...

Page 8: ...lication or supply regulator may be operating improperly See Gas Pressure section below HIGH ALTITUDE The water heaters covered in this Service Handbook are certified for elevations up to 10 100 feet...

Page 9: ...exceeding 14 W C under any upstream supply pressure or condition For Natural Gas BTH 120 250 models require a minimum gas supply pressure of 4 4 W C BTH 300 500 models require 4 8 W C and all models...

Page 10: ...he water heater is experiencing a sustained drop in supply gas pressure of 1 5 W C or more and the water heater is experiencing repeated Ignition Failure fault conditions intermittent loss of flame or...

Page 11: ...oint to end the heating cycle Use the Enable Disable Switch located on the front of the water heater and put the unit in disabled mode 11 Close the main gas shutoff valve serving the water heater 12 D...

Page 12: ...is energized the Control System enters the Input Verification operating state During Input Verification the Control System monitors all three pressure switches to ensure their contacts are in the cor...

Page 13: ...ween the two wiring terminals at each pressure switch see Figure below 5 After completing the tests confirm that all of the pressure switch wires are reconnected including the replacement part if nece...

Page 14: ...eset the Operating Temperature Set Point if it was adjusted Run the water heater through a complete heating cycle before leaving to ensure it is operating properly Draw water from the nearest faucet t...

Page 15: ...he tee with another piece of sensing tube 4 Restore power to the water heater if the water heater does not begin a heating cycle raise the Operating Set Point to activate a heating cycle 5 When the Co...

Page 16: ...r any restrictions or debris at the intake air termination outdoors Check for condensate water in the sensing tube switch if the sensing tube has water in it replace the Blocked Air Intake Switch and...

Page 17: ...ES The control has detected an open Blower Prover Pressure Switch during operation Blower Prover Pressure Switch sensing tube disconnected or kinked Loose or open wiring connections to Blower Prover P...

Page 18: ...the burner ignites briefly then shuts off with an Ignition Failure error message follow these steps Remove the connector from flame sense rod picture of connector showing location on unit Inspect the...

Page 19: ...lve problem If you do not see a brief blue flame through the sight glass during the ignition cycle at the moment the Gas Control Valve icon appears on the display follow these steps Remove and reinser...

Page 20: ...r meter This electrical signal will only last for 2 3 seconds if the burner does not ignite or the flame sensor does not detect ignition 24 VDC PRESENT If 24 VDC is present on the Gas Control Valve co...

Page 21: ...ional Your Company Name Here press DOWN for more CAUSES The Blocked Air Intake Switch has detected a possible restriction in the air intake pipe CHECK REPAIR Check pipe for restriction or excessive eq...

Page 22: ...sional Your Company Name Here press DOWN for more CAUSES The Blocked Exhaust Switch has detected a possible restriction in the exhaust pipe CHECK REPAIR Check pipe for restriction or excessive equival...

Page 23: ...roper operation If flame is not present cycle the unit Off by turning the Enable Disable switch to Disable wait for 5 seconds and cycle the unit On by turning the Enable Disable switch to Enable to se...

Page 24: ...ification or Heating operating states see Figure below 24 VAC should be present Note that the Gas Control Valve Voltage is only present for a short period of time during the ignition period 2 Check fo...

Page 25: ...n Page 2 SPARK IGNITER BURNER FLAME BURNER MUST BE GROUNDED CERAMIC INSULATOR FLAME SENSOR METAL CONDUCTOR CONTROL SYSTEM APPLIES AC CURRENT TO FLAME SENSOR AC CURRENT FLOWS FROM THE FLAME SENSOR TO T...

Page 26: ...ethod shown in Figure below Enable water heating and ensure a call for heat is active when the Control System energizes the 24 Volt Gas Control Valve the meter will measure flame sensing current durin...

Page 27: ...shown below CHECK REPAIR POWERED ANODES The water heaters covered by this Service Handbook are equipped with powered anodes BTH 120 models only use 1 powered anode all others will have two These anod...

Page 28: ...to allow for socket tool to fit properly REAR ANODE REPLACEMENT METHOD 1 Remove the two blower connectors from the blower remove gas valve power plug and the two wires from the low gas pressure switch...

Page 29: ...nk Note This is an alert The unit will continue to heat water in press DOWN for more CAUSES The controller has detected a low resistance or short to earth ground or the tank CHECK REPAIR Bent anode sh...

Page 30: ...y monitors the state of the ECO switch contacts If the ECO activates contacts open due to abnormally high water temperature the Control System will lock out and display Energy Cut Out ECO on the UIM S...

Page 31: ...rom the Temperature Probe see Figures on next page Compare the measured resistance to the values given in Temperatures Table below Temperature Probes are very reliable and should only be replaced when...

Page 32: ...d the tank temperature is known to be at or below 100 F 38 C replace the Temperature Probe Follow the draining and filling instructions in the maintenance section of the Instruction Manual that came w...

Page 33: ...Advanced button for press DOWN for more CAUSES The Upper or Lower Temperature Probe appears to be open very high resistance This fault code often means the connector has been corroded by cleaning che...

Page 34: ...tion Power Vent configurations derive all combustion air from the room where they are installed and discharge all flue gases to the outdoor atmosphere through a sealed vent exhaust pipe Power vent con...

Page 35: ...n collect inside and clog the Burner which can cause poor combustion sooting rough starting rough operation and Ignition Failure fault conditions and Control System lock outs The Burner is a radial de...

Page 36: ...the absence of local codes with the National Electrical Code ANSI NFPA 70 or the Canadian Electrical Code CSA C22 1 If any of the original wire as supplied on the water heater must be replaced it mus...

Page 37: ...eating is disabled The display CCB and other electrical components will still be energized and the display will read Water Heating Disabled The Enable Disable Switch can be used to disable operation a...

Page 38: ...nt piping are within the maximum equivalent lengths required in the Instruction Manual that came with the water heater Exceeding the maximum length or number of elbows allowed will also lead to Blocke...

Page 39: ...C from the Junction Box The CCB sends a signal from the J5 socket to a 5 pin wiring socket on the BTH 120 250 blower and VFD on the BTH 300 500 top cover control assembly The signal is an electronic i...

Page 40: ...n operating state If blower speed reduction does not occur during the Trial For Ignition operating state ensure the 5 pin plug from the CCB is securely plugged into the matching 5 pin socket on the bl...

Page 41: ...g VFD Hertz Readings for those rpms displayed on the VFD Note These models are capable of modulating their input rate Therefore the RPM readings can be in between the Heating Speed and Minimum Modulat...

Page 42: ...l control board that instructs the VFD to transmit the proper frequency to the blower to produce the proper blower speed and proper input Three conditions must be met for the frequency drive to start...

Page 43: ...a steel fiber jacket on the outer surface and is part of a larger Burner Assembly Figures below show side views of the complete Burner Assembly removed from the water heater with key components ident...

Page 44: ...ires at the three spade connectors connecting the blower to the VFD and unplug the blower speed feedback connector from the wiring harness 9 Disconnect the 24 Volt power wires to the Gas Control Valve...

Page 45: ...ounding rod see Figure below During trial for ignition the Control System powers a high voltage transformer Ignition Control from J6 and the Ignition Control supplies high voltage to the sparking rod...

Page 46: ...Socket on the CCB and the Burner Adapter are not broken pinched or disconnected Ensure there is approximately 120 VAC at the J6 Socket on the CCB It is a good practice to check for any crack or damag...

Page 47: ...orifice size BTH 120 thru 250 Models and all Natural gas models do not use a gas orifice ORIFICE CHART BTH 300 THRU 500 MODELS Model Series 300 200 201 400 200 201 500 200 201 Natural N A N A N A Prop...

Page 48: ...uit board Diagnostic and operational messages are generated by the CCB and sent to the UIM see UIM User Interface Module Screen on Page 54 Most of the water heater s components such as the Spark Ignit...

Page 49: ...lly unplugged Cover Removal Procedure Refer to CCB section on Page 47 for these instructions 1 Ensure power to the water heater is turned off 2 Remove the upper and lower temperature probe connectors...

Page 50: ...cian CCB CIRCUIT BOARD LAYOUT 11 12 1 J16 J5 J3 J13 J4 J17 J10 J9 J14 J15 J1 J6 J12 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 6 6 6 6 6 6...

Page 51: ...ommon 5 Not Used 6 AUX NO 7 AUX Common 8 Line Voltage 9 Neutral J5 Socket Blower Logic VFD Blower PIN DESCRIPTION 1 24V 2 PWM Signal 3 Not used 4 Blower Speed Feedback 5 Grounding J6 Socket 120V Out P...

Page 52: ...re Switch 9 Gas Control Valve 10 Gas Control Valve 11 24V 12 24V Return J15 Socket Pressure Switches PIN DESCRIPTION 1 Blower Prover Pressure Switch Blocked Air Intake Pressure Switch 2 Blocked Air In...

Page 53: ...52 Servicing should only be performed by a Qualified Service Technician WIRING DIAGRAM BTH 120 THRU 250...

Page 54: ...53 Servicing should only be performed by a Qualified Service Technician WIRING DIAGRAM BTH 300 THRU 500...

Page 55: ...inside the tank The second temperature on this screen is the Operating Set Point The Operating Set Point is the temperature at which the water heater will maintain the water inside the tank The third...

Page 56: ...TERS For additional information contact A O Smith Corporation 500 Tennessee Waltz Parkway Ashland City TN 37015 Tech Support 800 527 1953 Parts 800 433 2545 www hotwater com Copyright 2014 A O Smith W...

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