A.O. Smith 520 Direct Vent Indoor User manual

520 Indoor / 520 Outdoor Service Manual

Ver. 1.00

1

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

520 Indoor / 520 Outdoor Service Manual

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CONFIDENTIAL

Table of Contents

1.

Specifications………………………………………...…...………….……………………...…………………………

3

2.

Exterior view……………………...…….……………………………………………………………………………….

4

3.

Interior view…………………………….………………………………………………………………………………..

6

4.

List of main components in the interior view…….………………………………………………….……

8

5.

Schematic diagram…………………………………………………………………………………………………....

10

6.

Wiring diagram………………………………………………………………………………………………………….

11

7.

Wiring diagram checkpoints for diagnosis………………………..………………….………………….…

12

8.

(A) Resistance values of the temperature thermistors……..…………………………………………

(B) Resistance values of the temperature Exhaust thermistors…………………………………..

14

15

9.

Operational flow chart…………………………………………………………………………………………….…

16

10.

Component specifications………………...…………………………………………………………………….…

17

11.

Fault Analysis & Specifications…………………………………………………………………………………. 41

12.

Controls and settings……………………………………………………………………………………………….…

54

13.

Components diagrams………………………………………………………………..................................

89

14.

Parts list……………………………………………………………………………………………………………………..

92

15.

Revisions……………………………………………………...…………………………………………………………...

97

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1. Specifications of the 520 Direct Vent Indoor* and Outdoor

Model 520 Direct Vent Indoor 520 Outdoor

Dimensions H25.6"×W18.5"×D12.4"

Weight 73 lbs. 71 lbs.

Combustion

INPUT

BTU/h Max 199,000

Min 13,000

Combustion System

Power vent

Installation Direct-vent Outdoor

Fan motor PWM turbo fan

Manifold

Pressure**

Max

LP 4.9” WC

Natural 3.6” WC LP 4.6” WC

Natural 2.8” WC

Min

LP 1.0” WC

Natural 0.7” WC LP 0.9” WC

Natural 0.6” WC

Water control

Flow rate 0.5 GPM to 9.0 GPM

Available set

temperatures 100°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

(In, Out, Mixing, Exhaust) 3 thermistors

(In, Out, Mixing)

Operation

Remote controller

model 9007603005

PCB model 520

Indicators Red LED on PCB during operation & 3-digit 7-SEG LED

Power supply

control Surge absorber & Power ON-OFF switch

Features

Freeze protection

Ceramic heaters and Auto-firing system

Self

-

combustion

improvement

Air-Fuel Ratio Detection System

Easy-Link system

Yes (Up to 4 units)

Multiple-system N/A

* The 520 Direct Vent Indoor means the 520 Indoor in the text.

**The manifold pressure measurement is based on conditions without front cover.

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2. Exterior view

Top view Bottom view

Side view

Front view

520 Indoor

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Side view Front view

Bottom view

Top view

520 Outdoor

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3. Interior view

520 Indoor

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520 Outdoor

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4. List of main components in the interior view

No.

Description Item# in

components

diagram AOS Part # Common parts

For other models

1 Manifold assembly with

gas valve assembly 118 319143-046 (LP model)

319143-047 (NA model)

2 Computer board 701 319143-126

3 Igniter 123 319143-052 110, 310, 510, 910, 710

4 Transformer 702 319143-127 910

5 Water inlet 411 319143-074 710

6 Water outlet 435 319143-098 710

7 Mixing thermistor 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

Hi-limit switch 432 319143-095 510, 910, 710

13

Fan motor 114 319143-043 310 Indoor, 510 Indoor,

910, 710

14

Freeze protection

thermostat

704

319143

-

129

(

520

Indoor

)

719

319143

-

144

(

520

Outdoor

)

15

Flow sensor 429 319143-092 910, 710

16

Primary heat exchanger

assembly

401

319143

-

064

(

510

Indoor

)

456

319143

-

118

(

510

Outdoor

)

17

Gas inlet 121 319143-050 110, 310, 510

18

Pipe heater 426 319143-089

19

Water control valve 423 319143-086 910, 710

20

Secondary heat

exchanger 446 319143-108

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No.

Description Item# in

components

diagram AOS Part # Common parts

For other models

21

Outlet drain plug 416 319143-079 710

22

AFR rod 106 319143-035 310, 510, 910, 710

23

Flame rod 106 319143-035 310, 510, 910, 710

24

Igniter rod 108 319143-037 310, 510, 910, 710

25

Surge box 715 319143-140

26

Heater 101 405 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 motor for exhaust 124 319143-053

31

Hi-limit switch for

exhaust 442 319143-104

32

Exhaust thermistor

assembly 706 319143-131

33

Inlet drain plug (water

filter) 409 319143-072 910, 710

34

Flat heater 453 319143-115

35

3 array heater 454 319143-116

36

Case assembly 001

319143

-

009

(

510

Indoor

)

015

319143

-

023

(

510

Outdoor

)

37

Manifold port N/A N/A

38

Gas inlet port N/A N/A

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5. Schematic diagram

The diagram below refers to both the 520 Indoor and 520 Outdoor.

The 520 Outdoor doesn’t have the fan motor for exhaust, exhaust thermistor and hi-limit switch

for exhaust.

1. When a hot water tap is opened, cold water enters the 520 Indoor or 520 Outdoor.

2. The water flow sensor detects this water flow and sends this information to computer.

3. The computer initiates fan motor and sends signal to igniter to create ignition spark.

4. The main, proportional, and solenoid gas valves open to allow gas input.

5. The gas ignites and flames appear inside the burner chamber.

6. Water circulates through the heat exchanger and is heated up to the set temperature.

7. Using 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 Indoor controls the fan motor for exhaust and detects the exhaust temperature by using

the exhaust thermistor and hi-limit switch for exhaust during procedures of #3 to #8.

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6. Wiring diagram

The diagram below refers to both the 520 Indoor and 520 Outdoor.

A

A1

A2

B2

B1

C

C2 C1

D2

D1

E1

E3

E2

K1

F

G1

G2

H1

H2

I

J

K2

9007603005

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7. Wiring diagram check points for diagnosis

The table below applies to both the 520 Indoor and 520 Outdoor.

Check-

point

Part and Description Color of wires Normal range

A, A1

100V Power supply White – Black (A)

Brown – Brown (A1) 90 to 110 VAC

A2 120V Power supply Black - White 108 to 132 VAC

B1 Heater Black - 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 kΩ

Green - blue at COM (SV1) 78 to 100 VDC (during

operation) / 1.3 to 1.9 kΩ

Orange - blue at COM (SV2) 78 to 100 VDC (during

operation) / 1.3 to 1.9 kΩ

Red - blue at COM (SV3) 78 to 100 VDC (during

operation) / 0.9 to 1.7 kΩ

C1 Hi-limit switch Blue - Blue Less than 1 VDC

and

less than 1.0 Ω

C2 Overheat cutoff fuse Blue - Blue Less than 1 VDC

and

less than 1.0 Ω

D1 Easy-link connectors Red – Red

Blue - Blue 15 VDC

(during Easy-link operation)

D2 White - White

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Check-

point

Part and Description Color of wires Normal range

E1 Mixing thermistor Black - Black See table on p. 14 E2 Output thermistor Black - Black

E3 Inlet thermistor Black - Black

F Remote controller * 11 to 25 VDC

G1 Fan motor Red – Blue

Yellow – Blue

Orange - Blue

110 to 160 VDC

13 to 17 VDC

2 to 6.5 VDC

G2 Fan motor for exhaust

H1 Gas proportional valve White - red

1 to 15 VDC

(during operation)

and

20 to 40 Ω

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 computer board)

More than 1 μA

(during operation)

Flame rod Orange - Flame rod

(Between flame rod and

the computer board)

More than 1 μA

(during operation)

J Water control valve

Blue – Brown

Orange – Brown

Red – Brown

13.0 to 16.0 VDC

ON: 12.5 to 16.0 VDC

OFF: 0 to 1 VDC

1 VDC Less ( 0° position)

K1 Exhaust thermistor White - White See table on p. 15

K2 Hi-limit switch for exhaust White - White Less than 1 VDC

and

less than 1.0 Ω

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CONFIDENTIAL

8. (A) Resistance values of the temperature thermistors

The 520 Indoor and 520 Outdoor use the same thermistors.

Resistance values at different temperatures

ºF 32 41 50 59 68 77 86 95 104 113

ºC 0 5 10 15 20 25 30 35 40 45

Resistance kΩ23.76 19.08 15.43 12.56 10.28 8.47 7.02 5.85 4.90 4.12

Temperature ºF 122 131 140 149 158 167 176 185 194 203 212

ºC 50 55 60 65 70 75 80 85 90 95 100

Resistance kΩ3.49 2.96 2.53 2.16 1.86 1.60 1.39 1.21 1.05 0.92 0.81

Temperature / ºF vs Resistance / kΩ

Temperature / vs Resistance / kΩ

Temperature

0.00

5.00

10.00

15.00

20.00

25.00

20 40 60 80 100 120 140 160 180 200 220

Temperature / ºF

Resisitance / kΩ

0.00

5.00

10.00

15.00

20.00

25.00

0 10 20 30 40 50 60 70 80 90 100

Temperature / ºC

Resisitance / kΩ

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8. (B) Resistance values of the temperature Exhaust thermistor

Only the 520 Indoor is equipped with the exhaust thermistor.

Resistance values at different temperatures

ºF 32 41 50 59 68 77 86 95 104 113

ºC 0 5 10 15 20 25 30 35 40 45

Resistance kΩ30.04 24.12 19.50 15.87 13.00 10.71 8.87 7.39 6.19 5.21

Temperature ºF 122 131 140 149 158 167 176 185 194 203 212

ºC 50 55 60 65 70 75 80 85 90 95 100

Resistance kΩ4.41 3.74 3.19 2.73 2.35 2.03 1.76 1.53 1.33 1.16 1.02

Temperature

Temperature(°F) vs. Resistance(kΩ)

Temperature(° ) vs. Resistance(kΩ)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

20 40 60 80 100 120 140 160 180 200 220

Temperature / ºF

Resisitance / k

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

0 10 20 30 40 50 60 70 80 90 100

Temperature / ºC

Resisitance / k

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9. Operational flow chart

The diagram below refers to both the 520 Indoor and 520 Outdoor.

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10. Component specifications

10-1.

Burners……………………..………………………………….………………………………....……….

18

10-2.

Gas manifold………….………………………………………………..…………………………….....

19

10-3.

Fan motor……………………………………………………………………………………….……...…

20

10-4.

Fan motor for exhaust……………………………………………………………………………….

21

10-5.

Gas valve assembly………………..……………………….………………………………..……….

22

10-6.

Flame rod………………………………………………………….……………………………………….

23

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

10-15.

Hi-limit switch for exhaust………………………………………………………………………...

33

10-16.

Overheat cutoff fuse…..………………………………………………………….....................

34

10-17.

Freeze protection heaters…………….……………………………………………………………

35

10-18.

Computer board……………….………………………………………………………………….……

36

10-19.

Transformer. ………...…………………………………………………………………………………..

37

10-20.

Igniter………………………………………………………………………………………………………..

38

10-21.

Freeze protection thermostat………………………………………………………….………..

39

10-22.

Surge box……………………………………………………………………………………………….... 40

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10-1. Burners

Unit Part # #101 AOS Part # 319143-030

Checkpoint N/A

Function

There are 2 types of burners in the water heater: the gas-rich burner

stabilizes the flames within the combustion chamber and the air-rich burner

produces more heat in the combustion chamber. The burners facilitate the

air/gas mixture necessary to produce the proper heat during the

combustion reaction.

Failure events

1. Unable to initialize/sustain combustion

2. Dust 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 flame loss.

3. Ignition failure.

4. Back-firing.

Error codes when the

burners fails

101 111 121 991

Diagnostic Visual inspection: excessive dust deposit on the burner surface and/or

unstable flame conditions during operation.

Color/Number of wires N/A

The burner for the 520 Indoor and 520 Outdoor has the “46V” mark as shown below.

The burner damper is not

included in 319143-030.

Burner damper (#111 / 319143-040)

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10-2. Gas manifold

Unit Part # Included

in #118 AOS Part # 319143-046 (LP)

319143-047 (NG)

Checkpoint N/A

Function

1. The manifold distributes gas from the gas valves to the burners. The

manifold has two types of the nozzles: one type for gas-rich burners (16

nozzles) and the other for air-rich burners (15 nozzles)

2. There are 3 zones within the manifold, to ensure efficient combustion

operation.

Failure events

1. Dust deposit on the manifold.

2. Gas leakage from a failed manifold.

3. Ignition failure.

4. Imperfect combustion.

Effects on the water

heater if the manifold

fails

1. The burners cannot receive proper gas flow from the manifold, which can

cause 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 the

manifold fails 101 111 121 991

Diagnostic 1. Visual inspection: Excessive dust deposit around the nozzles or cracks on

the manifold.

2. Check voltages and resistance: proper range of values shown below.

Color/Number of wires Blue-Red 78 to 100 VDC / 0.9 to 1.7 kΩ

Nozzles for gas-rich burners

Nozzles for air-rich burners

319143-046 (for LP model)

and 319143-047 (for NA

model) is an assembly of the

gas manifold with the gas

valve assembly. For safety

reasons, these assemblies

should be installed in the

unit as a whole set.

The gas manifold for the LP

has the “46V” mark, and the

gas manifold for the NA has

the “59J” mark on the

manifold plate.

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10-3. Fan motor

Unit Part # #114 AOS Part # 319143-043

Checkpoint G1

Function To provide combustion air into the combustion chamber and to exhaust flue

gas.

Failure events

1. Fan speed failure, causing abnormal sounds with or without combustion

during operation.

2. Unexpected activation caused by the connectors of the fan motor getting

wet.

3. Disconnects from the bottom of the combustion chamber

Effects on the water

heater if fan motor fails

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. Visual inspection: connection/breakage of wires or dust (causing electrical

shortage)

2. Voltage check: proper range of voltages shown below.

Color/Number of wires

Red-Blue 110 to 160 VDC (Input)

Yellow-Blue 13 to 17 VDC (Input)

Orange-Blue 2.0 to 6.5 VDC (Input)

White-Blue Verify the fan motor speed using the Diagnostics Mode of

the 520 models computer board or the 9007603005

temperature remote controller. See Section 12-1 for details.

PWN turbo fan motor

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A.O. Smith 520 Direct Vent Indoor User manual

A.O. Smith 520 Direct Vent Indoor User manual

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