A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual Download

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520 Indoor / 520 Outdoor Service Manual

Ver. 1.00

CONFIDENTIAL

520 Direct Vent Indoor

and Outdoor Models

On-Demand Water Heater

Service Manual

Water Heater

Model 520 Direct Vent Indoor

Water Heater

Model 520 Outdoor

A.O. Smith Water Products Company
500 Tennessee Waltz Parkway
Ashland City, TN 37015
Toll Free: 1-877-737-2840

Summary of Contents for Water Heater 520 Direct Vent Indoor

Page 1: ...520 Direct Vent Indoor and Outdoor Models On Demand Water Heater Service Manual Water Heater Model 520 Direct Vent Indoor Water Heater Model 520 Outdoor A O Smith Water Products Company 500 Tennessee...

Page 2: ...chematic diagram 10 6 Wiring diagram 11 7 Wiring diagram checkpoints for diagnosis 12 8 8 A Resistance values of the temperature thermistors B Resistance values of the temperature Exhaust thermistors...

Page 3: ...0 F to 185 F default 120 F Temperature on the unit settings 100 F 105 F 110 F 115 F 120 F 125 F 135 F 140 F 145 F 150 F 155 F 160 F 165 F 170 F 175 F 185 F Bypass valve Yes Thermistors 4 thermistors I...

Page 4: ...9 1 m m I N T A K E 2 3 4 7 1 8 m m E X H A U S T 12 1 2 3 16m m 2 5 1 2 6 4 9 m m 120 VAC 2 1 4 58mm 4 5 8 1 17mm G AS Mal e 4 10 1mm 4 10 2m m Fem ale 3 4 1 9mm Cond ens ate dr ai n po rt Con den sa...

Page 5: ...2 320 m m 4 1 2 1 15m m 4 1 2 11 5 mm 4 5 8 1 1 7m m G A S 12 0V A C 2 1 4 5 8 2m m H OT 5 5 8 1 42 mm 6 1 4 1 59 mm Co nd e ns a te d ra i n po r t 29 1 2 7 5 1m m 1 1 4 29 2 m m C OL D 2 5 1 2 6 5...

Page 6: ...520 Indoor 520 Outdoor Service Manual Ver 1 00 6 CONFIDENTIAL 3 Interior view 520 Indoor 20 32 16 10 18 24 11 15 3 19 37 38 17 33 5 8 27 6 7 21 23 30 31 9 1 13 25 2 22 4 12 14 28 29 26 26 35 35 34 36...

Page 7: ...520 Indoor 520 Outdoor Service Manual Ver 1 00 7 CONFIDENTIAL 520 Outdoor 1 3 4 5 6 27 7 8 9 2 11 13 15 16 17 19 20 21 22 23 24 25 29 28 10 12 33 37 38 26 18 35 34 35 26 14 36...

Page 8: ...tor 418 319143 081 710 8 Inlet thermistor 422 319143 085 510 910 710 9 Output thermistor 433 319143 096 510 910 710 10 Overheat cut off fuse 404 319143 067 11 Burner assembly Burners 101 319143 030 12...

Page 9: ...319143 068 910 710 27 Outlet heater 415 319143 078 110 310 510 710 28 Over heat cut off fuse for combustion chamber 008 319143 016 710 29 Secondary heat exchanger drain plug 458 319143 120 30 Fan moto...

Page 10: ...thermistors to measure temperatures the computer modulates the gas and water valves to ensure proper output water temperatures 8 When the tap is closed the 520 Indoor or 520 Outdoor shuts down 520 In...

Page 11: ...2 3 4 5 6 O F F 7 8 2 1 W Y O R Gas Propor tional Valve W R W R BK R W Flow Sensor BK W R Hi limit switch for exhaust Exhaust thermistor W W W R YG W BK BR R O Y G W BK BL Water Control valve Igniter...

Page 12: ...Black 90 to 110 VAC B2 Igniter Purple Purple 90 to 110 VAC C Gas valves Light blue blue at COM MV 78 to 100 VDC during operation 0 9 to 1 3 k Green blue at COM SV1 78 to 100 VDC during operation 1 3 t...

Page 13: ...valve White red 1 to 15 VDC during operation and 20 to 40 H2 Flow sensor Red Black 4 to 5 5 VDC White Black GND 1 to 4 VDC 1 200 pulse min I Air fuel ratio rod Yellow AFR rod Between AFR rod and the...

Page 14: ...ce k 23 76 19 08 15 43 12 56 10 28 8 47 7 02 5 85 4 90 4 12 Temperature F 122 131 140 149 158 167 176 185 194 203 212 C 50 55 60 65 70 75 80 85 90 95 100 Resistance k 3 49 2 96 2 53 2 16 1 86 1 60 1 3...

Page 15: ...04 24 12 19 50 15 87 13 00 10 71 8 87 7 39 6 19 5 21 Temperature F 122 131 140 149 158 167 176 185 194 203 212 C 50 55 60 65 70 75 80 85 90 95 100 Resistance k 4 41 3 74 3 19 2 73 2 35 2 03 1 76 1 53...

Page 16: ...ircuit failure 031 blink 321 blink 701 blink 510 blink 611 blink Fan motor stop operation 721 blink False flame Igniter OFF Reignition Success OuTH OPEN or SHORT Fan motor fault MV OFF SV2 OFF GPV OFF...

Page 17: ...3 10 7 AFR rod 24 10 8 Heat exchanger 25 10 9 Secondary heat exchanger 26 10 10 Flow sensor 27 10 11 Water control valve 28 10 12 Thermistors 30 10 13 Exhaust thermistor 31 10 14 Hi limit switch 32 10...

Page 18: ...t or soot deposit on the burner surface 3 Cracks on the burners 4 Gas leakage from the burners Effects on the water heater if burners fails 1 Unexpected combustion 2 Unstable flame conditions and or f...

Page 19: ...ause poor combustion in the combustion chamber In this case the AFR rod will detect an improper flame condition and computer will take safety measures 2 Gas leakage from the manifold Error codes when...

Page 20: ...ails 1 The water heater does not function properly 2 Failure to ignite or abnormal ignition 3 Unstable combustion conditions Error codes when the fan motor fails 101 111 121 611 991 Diagnostic 1 Visua...

Page 21: ...gas temperature Error codes when the fan motor fails 621 520 Indoor only 941 520 Indoor only Diagnostic 1 Visual inspection connection breakage of wires or dust causing electrical shortage 2 Voltage c...

Page 22: ...ction breakage of wires 2 Listen for clunk sounds from the gas valves opening right after fan motor initiates 3 Check voltages and resistance of coils proper range of values shown below Color Number o...

Page 23: ...or 121 error code s will display 2 The water heater will not initiate the ignition process The 721 error code will display Error codes when the flame rod fails 111 121 721 Diagnostic 1 Visual inspecti...

Page 24: ...and or 121 error code s will display 2 The water heater will not initiate the ignition process The 721 error code will display 3 The fan motor speed cannot be modulated properly under abnormal flame c...

Page 25: ...ce to detect this event and immediately stop the water heater from operating 3 Abnormal sounds during combustion Error codes when the heat exchanger fails N A Diagnostic 1 Visual inspection soot depos...

Page 26: ...ger 2 Leaking exhaust gas Effects on the water heater if the secondary heat exchanger fails 1 Water leakage from the secondary heat exchanger 2 Exhaust gas leakage 3 Abnormal sounds during combustion...

Page 27: ...if flow sensor fails Ignition sequence does not start 520 Indoor 520 Outdoor will not initiate any operation Error codes when the flow sensor fails 441 Within Easy link systems only Diagnostic 1 Visua...

Page 28: ...tion The function of the bypass valve 4 Prevents water from flowing through the heat exchanger when the water heater is not in operation to protect the heat exchanger The function of the two way valve...

Page 29: ...ve and bypass valve Color Number of wires Blue Brown 13 0 to 16 0 VDC Orange Brown ON 12 5 to 16 0 VDC OFF 0 to 1 VDC Red Brown 0 position 1 VDC less The water control valve contains the flow adjustme...

Page 30: ...he water heater will have temperature fluctuations in hot water Error codes when thermistors fails 311 Output 321 Inlet 331 Mixing Diagnostic 1 Visual inspection connection breakage of wires and or de...

Page 31: ...resistance values are just off the 341 error codes will display Error codes when exhaust thermistor fails 341 520 Indoor only Diagnostic 1 Visual inspection connection breakage of wires and or debris...

Page 32: ...e heat exchanger exceeds 194 F 90 C Note The mixing and output thermistors always act as backup hi limit detectors to detect excessively high water temperatures in the heat exchanger 2 The water heate...

Page 33: ...for exhaust fails 1 Unable to shut down the water heater if the exhaust gas temperature in the exhaust chamber exceeds 151 F 66 C 2 The water heater is always shut down immediately after the ignition...

Page 34: ...instantly The 111 121 or 711 error code will display Failure events 1 Unable to detect the excessively high temperatures within the water heater Effects on the water heater if the overheat cutoff fuse...

Page 35: ...age needed to heat up Effects on the water heater if heater fails Ceramic heaters do not activate allowing water contained in the heat exchanger to freeze up possibly causing the heat exchanger to bur...

Page 36: ...uter Effects on the water heater if the computer board fails A component s may not operate within the water heater In most cases of computer board failure the whole the water heater does not operate a...

Page 37: ...C Effects on the water heater if transformer fails 1 The water heater does not operate due to lack of power from transformer 2 A failed transformer can cause electrical damage to other electrical comp...

Page 38: ...eater cannot ignite during the ignition process and the 111 or 121 error codes will display 2 No effects on the water heater however the durability of the igniter wears down Error codes when Igniter f...

Page 39: ...rotection thermostat fails 1 The freeze protection heaters will always be ON causing heat damage to components inside the water heater 2 The freeze protection heaters will never be able to turn on eve...

Page 40: ...failure of the absorber Effects on the water heater if the Surge box fails 1 Unable to protect the computer board if high voltage gets applied to the unit The computer board can short out stopping al...

Page 41: ...en F 6 Disconnection short circuit grounding of remote wires Normal 11 to 25 VDC between 7 Fault of PCB of remote control 1 Check for normal voltage at terminal It takes long time to get hot water at...

Page 42: ...as out of the flue Abnormal sound from water heater 1 Check the gas type of the water heater 2 Check how long the water heater has been installed and in use 3 Check the installation place 4 Check the...

Page 43: ...e brown Normal ON 12 5 to 16 0 V OFF 0 to 1 V between orange brown Normal 1 VDC less 0 position between red brown J 7 Fault of Water control valve Normal 0 09 to 0 2 k between red black J Error Code M...

Page 44: ...n 10 20 Visual inspection connection breakage of wires and or observed weak spark 1 Cracks soot on igniter rod 2 Improper gap between burner igniter rod Normal gap 0 16 4mm 3 PCB fault Normal 90 to 11...

Page 45: ...ult During operation more than 1 A through the flame rod wire orange I 8 Check if hi limit switch is properly functioning Error Code Malfunction description Cancellation method 121 Error code is shown...

Page 46: ...1 Output thermistor fault Refer to section 10 12 Visual inspection connection breakage of wires and or debris on thermistor Check voltage resistance between black black 12 Refer to Section 8 A for pr...

Page 47: ...er to Section 8 B for proper range of values K1 Error Code Malfunction description Cancellation method 391 Disconnected AFR rod Turn off the power or water supply Diagnosis Checkpoint 1 AFR rod fault...

Page 48: ...rmal 78 to 100 VDC between COM blue 73 red during operation Visual inspection of PCB connection breakage of wires and or burn marks on the computer board 2 Gas solenoid valve fault MV SV1 SV2 and or S...

Page 49: ...urn marks on the computer board G1 Error Code Malfunction description Cancellation method 621 Exhaust fan motor fault 520 Indoor only Turn off the power or water supply Diagnosis Checkpoint 1 PCB and...

Page 50: ...nal pump Turn off the power Diagnosis Checkpoint 1 Check whether the pump connected to PCB works properly Error Code Malfunction description Cancellation method 651 Water control valve fault Flow adju...

Page 51: ...OFF 0 to 1 V Normal 1V Less than 0 position Visual inspection PCB connection breakage of wires and or burn marks on the computer board J Error Code Malfunction description Cancellation method 701 1 PC...

Page 52: ...between blue blue C2 2 PCB and or gas valve fault Refer to section 10 5 10 18 Visual inspection PCB connection breakage of wires and or burn makes on the computer board C Error Code Malfunction descri...

Page 53: ...old pressure in the water heater 6 Check if the exhaust fan motor works properly 7 Check if the set temperature is higher than 140 F 60 C and the system is recirculation Recirculation system with high...

Page 54: ...Easy link system 70 12 8 B Pump control ON OFF conditions BTU requirements 71 12 9 Multi unit system ON OFF conditions 72 12 10 Operation time for unit rotation 73 12 11 12 12 Individual unit operati...

Page 55: ...refer to the table on p 58 and p 60 for the proper mode In the tables on p 58 to p 60 say the followings d1 to d18 p 58 to p 59 Unit information of Individual 520 Indoor or 520 Outdoor h1 to h15 p 60...

Page 56: ...sing the HOT or COLD buttons Fig 1 shows mode 5 being selected When selecting information please refer to the table on p 58 and p 59 for the proper mode 3 Press the INFO button to select the mode and...

Page 57: ...k system of the 520 Indoors or 520 Outdoors a maximum of four units of the 520 Indoor or 520 Outdoor s can be linked together 4 Press the INFO button to select the desired unit 5 When the desired unit...

Page 58: ...osed position 0 Ratio of hot water and cold water d10 0 to 999 10 0 to 999 Error code history displays most recent error code d11 Error code history displays most recent error code 11 Error code histo...

Page 59: ...urs Estimated output from Computer board d29 0 to 999 1000 BTU h 29 0 to 9 999 100 BTU Actual output of Unit d30 0 to 999 1000 BTU h 30 0 to 9 999 100 BTU Integrating flow of Unit d31 0 to 999 10000 g...

Page 60: ...to 720 minutes After 720 the next rotation occurs h7 0 to 720 minutes After 720 the next rotation occurs ON OFF cycles during current rotation h8 0 to 100 cycles After 100 the next rotation occurs h8...

Page 61: ...k White If no voltage is detected going into the computer board the fuse box or transformer might have malfunctioned or been damaged If 100 VAC is measured going into the computer board and the water...

Page 62: ...had prior error codes the 3 digit 7 seg LED will display the most recent error code first Pressing the button again will display the 2nd most recent error code and so on Computer saves a maximum of 1...

Page 63: ...per sticking Vent Flaps installed on the Termination Snow build up around Termination Installed in a closet No Ventilation or lack of combustion air 6 If installed in laundry room check the burner and...

Page 64: ...higher than the normal value the FM speed is increased If the AFR value is lower than the normal value the FM speed is decreased These values are read with the front cover close Measure the values af...

Page 65: ...f Individual operation mode See Section 12 11 Enable Default Disable 5 6 Pump mode 7 The number of priority unit in a 520 Indoor or 520 Outdoor Two priority units One priority unit Default 8 Deactivat...

Page 66: ...is increased automatically See section 12 12 Fan motor for combustion No 5 OFF position ON position No 6 OFF position 0 6 ON position 12 18 Fan motor for exhaust 520 Indoor only No 5 OFF position ON...

Page 67: ...he computer board of all child units for at least 5 seconds 2 The 3 digit 7 seg LED on the computer board of all child units will display 0 to signify that the computer memory has been erased of its p...

Page 68: ...heater ON OFF Conditions Conditions needed to turn ON The BTU requirement is more than 14 880 BTU h AND The water flow rate is more than 0 5 GPM Conditions needed to turn OFF The BTU requirement is l...

Page 69: ...F C ON OFF table Set temperature F Flow rate GPM 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 100 ON 40 5 70 2 80 2 85 1 88 1 90 1 91 5 92 6 OFF 52 4 76 2 84 1 88 1 90 5 92 1 93 2 94 0 115 ON 55 5 85 2 95 2 100 1...

Page 70: ...These functions enable the re circulation pump to be controlled by the following conditions ON OFF Conditions Re circulation mode Energy conserving re circulation mode Conditions that activate the pum...

Page 71: ...lation example Set temperature Tset 120 F Flow rate 2 5 GPM Condition needed to turn the pump ON 120 Tin 2 5 500 14 880 Tin 108 1 F Condition needed to turn the pump OFF 120 Tin 2 5 500 14 880 Tin 108...

Page 72: ...F C GPM L min 100 120 38 49 3 4 13 125 130 52 54 3 2 12 140 60 2 9 11 145 150 63 65 2 6 10 155 185 68 85 2 4 9 2 Condition required to reduce the number of activated 520 Indoors or 520 Outdoors A In t...

Page 73: ...ter 12 hours of operation NOTE The priority unit is the unit that turns on first when there is a hot water demand When there is a black out and or cut off for over 50 minutes priority unit will switch...

Page 74: ...der normal conditions 0 5GPM When the parent unit fails 0 5 4 2 0GPM Minimum flow rate of the easy link system depends on the number of the units installed in the easy link system The set temperature...

Page 75: ...motor speed increased by 3 6 520 Outdoor Left bank of dipswitches No 5 ON No 6 OFF 2 4 000 to 5 000ft FM function the fan motor speed increased by 12 520 Indoor the fan motor speed increased by 7 3 52...

Page 76: ...witches See section 12 5 for dipswitch settings NOTE Changing the temperature display unit on the PCB does not change the unit of the remote controller display To convert between C and F displays on t...

Page 77: ...mponents are always monitoring exhaust gas conditions in order to prevent heat damage to PVC Plastic venting If the exhaust gas temperature exceeds 140 F these components will enable the unit to safel...

Page 78: ...ll not exceed 1 amp For example To the right there is a sample of relay specifications from an arbitrary brochure You can select either the 120 VAC or 240 VAC relay because their current values are le...

Page 79: ...520 models computer detects any error codes the alarm port terminal on the 520 models computer will activate the connected lamp or buzzer How to reset the operation Clear the current error code Refer...

Page 80: ...ctivate its operation If presence of a gas leak is detected immediately shut off the 520 Indoor or 520 Outdoor and inspect the tube manifold connection otherwise proceed onto the next step 5 Press and...

Page 81: ...ease or decrease the manifold gas pressure respectively Figure 3 Refer to the manometer to verify that pressure has been set to desired value 6 After gas pressure has been set deactivate the 520 Indoo...

Page 82: ...ontroller display mode 3 fan motor speed by entering the Diagnostics mode Refer to Section 12 1 3 Press and hold down the MAX button on the computer board While holding down the MAX button press eithe...

Page 83: ...motor for combustion 10 0 5 0 1 0 0 1 0 5 0 10 0 Fan motor for exhaust 6 3 0 6 0 0 6 3 6 Figure 1 Left bank of dipswitch settings Figure 2 520 models Computer board 1 2 3 4 5 6 7 8 FM N O 9 10 Unit MA...

Page 84: ...lusive because they focus on different areas of the 520 Indoor or 520 Outdoor As long as each particular feature s activation requirements are met it is possible for both features to operate at the sa...

Page 85: ...Yes 46 F and above 37 F and below YES Ceramic heating blocks The blocks will only activate based on what the freeze protection thermostat senses The thermostat is located on the intake port for 520 In...

Page 86: ...Outdoor will display P on its three 7 seg LED however the 9007603005 remote controllers will not display anything on its screen In order to detect the temperature of the system accurately The compute...

Page 87: ...ode cannot be in combustion forced combustion or FM adjustment modes press and hold the Increase button for at least 5 seconds or longer to enter Diagnostic Mode 4 Scroll through the needed informatio...

Page 88: ...l water flow has ceased close all hot water taps 6 Have a bucket or pan to catch the water from the drain plugs of the 520 Indoor or 520 Outdoor Unscrew the drain plugs to drain all the water out of t...

Page 89: ...3 052 702 152 005 002 051 008 009 004 152 052 011 012 013 014 010 052 152 152 124 152 704 156 015 007 054 006 703 052 004 702 152 005 016 051 008 009 004 152 052 010 052 Other than the case assembly N...

Page 90: ...7 16 055 7 17 053 053 0 55 053 713 71 1 71 5 71 9 001 719 101 102 103 1 04 1 05 106 107 108 109 1 10 11 1 1 12 1 14 116 117 11 8 119 120 121 122 123 151 1 52 152 1 52 152 710 15 2 152 1 55 155 054 153...

Page 91: ...1 52 052 4 27 427 4 20 452 A C 414 420 4 06 450 417 426 450 417 45 5 452 455 15 0 4 37 443 43 1 C 45 1 150 437 443 152 45 3 15 2 12 7 1 26 4 05 4 54 4 54 454 44 9 444 447 0 10 457 458 46 3 4 62 46 2 4...

Page 92: ...43 018 Condensate drain port 011 319143 019 Duct 012 319143 020 Duct gasket A 013 319143 021 Duct gasket B 014 319143 022 Duct cover plate 015 319143 023 Case assembly Out 016 319143 024 Front cover O...

Page 93: ...10 310 510 910 118 319143 046 Manifold assembly with gas valve assembly LP 319143 047 Manifold assembly with gas valve assembly NA 119 319143 048 Wire clamp 60 110 310 510 910 710 120 319143 049 Gas i...

Page 94: ...ort 407 319143 070 Filter plug 910 710 408 319143 071 O ring P25 FKM 409 319143 072 Water inlet filter 910 710 410 319143 073 O ring JASO 1021 FKM 411 319143 074 Water inlet 710 412 319143 075 O ring...

Page 95: ...O ring JASO 1017 FKM 437 319143 100 O ring P14 FKM 438 319143 101 Drain tube 440 319143 102 Secondary heat exchanger plate gasket A 441 319143 103 Secondary heat exchanger plate gasket B 442 319143 1...

Page 96: ...128 Junction box inner plate 110 310 510 704 319143 129 Freeze protection and EH IG wire IN 705 319143 130 Gas valve wire 706 319143 131 Exhaust thermistor assembly 707 319143 132 Thermistors wire 70...

Page 97: ...520 Indoor 520 Outdoor Service Manual Ver 1 00 97 CONFIDENTIAL 15 Revisions Version Description of changes Date 1 00 First edition 11 01 10...

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