A.O. Smith 710 ASME User manual

710 / 710 ASME Service manual
Ver. 1.00
1
CONFIDENTIAL
710 / 710 ASME
On-demand Water Heater
Service manual
A.O. Smith Water Products Company
500 Tennessee Waltz Parkway
Ashland City, TN 37015
Toll Free: 1
-
877
-
737
-
2840
710 models

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CONFIDENTIAL
Table of Contents
1.
Specifications………………………………………...…...………….……………………...…………………………
3
2.
Exterior view…………………………………………………………………………………………………………….. 4
3.
Interior view….………………………………………………………………………………………………………….. 5
4.
List of main components in the interior view………………………………….………………………….
6
5.
Schematic diagram…………………………………………………………………………………………..……….. 8
6.
Wiring diagram…………………….………………………………………………………………………..…………. 9
7.
Wiring diagram checkpoints for diagnosis……………………………………………………………….…
10
8.
Resistance values of the temperature thermistors……………..………………………………………
12
9.
Operational flow chart..……………………………………………………………………………………………..
13
10.
Component specifications…………………………………………………………………………………………. 14
11.
Fault Analysis & Specifications……………………………………………………………........................ 35
12.
Controls and settings………………………………………………………………………………………………….
46
13.
Components diagrams……………………………………………………………….................................. 75
14.
Parts list……………………………………………………………………………………………………………………..
78
15.
Revisions…...................................…………………………...………………………………..…………………
82

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CONFIDENTIAL
1. Specifications
Unit Model 710 / 710 ASME
Unit dimensions H 23.6"×W 18.5"×D 8.9"
Weight 59 lbs.
Max 240,000
INPUT
BTU/h
Min 24,000
Combustion System
Power vent
Installation Indoor, Outdoor, Direct vent
Fan motor PWM Turbo fan
Max LP 3.4”WC
Natural 2.3”W.C
Combustion
Manifold
Pressure*
Min LP 0.7 WC
Natural 0.5”WC
Flow rate 0.5 to 9.0 GPM
Available set temp.
100°F to 185°F
default set 120 °F
Temperature
dipswitch setting
100°F, 115°F, 120°F, 135°F, 145°F, 155°F, 165°F, 185°F
Bypass valve Yes
Water control
Thermistors 3 thermistors (In, Out, Mixing)
Available remote
controller Part # 9007603005
PCB Model T-M32 (Part #319143-279)
Indicators Red LED on PCB during operation & 7-seg LED
Operation
Power supply
control GFI & Surge absorber
Freeze protection
Ceramic heaters and Auto- FM system
Self-combustion
improvement Air Fuel Ratio detection system
Easy-link system
Yes
Future
Multi-unit system
Yes
*The manifold pressure measurement is base on conditions without front cover.

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4" ( 1 01mm)
7" (17 9mm)
15-3 /4" (399mm)
18-1 /2" (470mm)
23-5 /8" (600mm)
24-5 /8"(626 mm)
4-1/2" (11 4mm)
1-1/ 8" (27.8mm )
COLD 3- 1/8" (80 .8mm )
HOT 4-5/8 " (1 18.3mm)
GAS 6-1/4" (159mm)
8-7/ 8" (226mm)
120 VAC 5-1/2 "( 142mm )
5-1/ 2"(142mm)
5-3/ 4"(147mm)
COLD 1-5/ 8"(40.9mm)120 VAC 1 -5/8" (42mm)
GAS 5-7/8"(1 47.9mm)HOT 5-7/8"(149mm )
GAS 6-1/4"(159mm )
CO LD 3-1 /8"(80.8mm )
HOT 4-5/8 "(11 8.3mm)
120 VAC 5 -1/2 "(1 41.6mm)
2. Exterior view
Side view Front view
Top view Bottom view

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3. Interior view
16
20
1
3
4
5
678
9
10
11
12
13
14
15
17
18
19
21
2
22
23
24 25
26
27
28
29

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4. List of main components in the interior view
No. Description
Items# in
components
diagram
AOS
Part #
Common parts
For other models
1 Case assembly 001 319143-287
2 Manifold assembly with gas
valve assembly 120 319143-305 (LP model)
319143-306 (NA model)
3 Computer board 701 319143-279
4 Igniter 125 319143-052 520, 110, 310, 510,
910
5 Transformer 702 319143-309
6 Water inlet 411 319143-074 520
7 Water outlet 435 319143-098
8 Mixing thermistor 418 319143-081 520
9 Inlet thermistor 422 319143-085 520, 510, 910
10 Output thermistor 433 319143-096 520, 510, 910
11 Overheat cut-off fuse 403 319143-286
12 Burner assembly (Burners) 101 319143-299
13 Hi-limit switch 432 319143-095 520, 510, 910
14 Fan motor 115 319143-043 520, 310, 510, 910
15 Freeze protection thermostat
117 319143-185 110, 310, 510
16 Flow sensor 429 319143-092 520, 910
210 319143-302
(Regular model)
17 Heat exchanger
211 319143-314
(ASME model)
18 Gas inlet 123 319143-307
19 Heater 410 319143-068 520, 910
20 Water control valve 423 319143-086 520, 910
21 GFI 712 319143-227 910

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No. Description
Items# in
components
diagram
AOS
Part #
Common parts
For other models
22 Outlet drain plug 416 319143-079 520
23 Air-fuel ratio rod (AFR rod) 106 319143-035 520, 310, 510, 910
24 Flame rod 106 319143-035 520, 310, 510, 910
25 Igniter rod 108 319143-037 520, 310, 510, 910
26 Surge box 715 319143-284 910
27 Inlet drain plug (water filter) 408 319143-072 520, 910
28 Manifold port N/A N/A
29 Gas inlet port N/A N/A

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5. Schematic diagram
1. When a hot water tap is opened, cold water enters the 710.
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 710 shuts down.
Output Thermistor
Gas proportional valve
Gas solenoid valve 2
Gas solenoid valve 1
Gas solenoid valve 3
Water control
valve
Mixing Thermistor
Igniter rod
Heat
Exchanger
Gas
Hi-limit switch
Flow sensor
Exhaust
O.H.C.F
Main gas valve
Burner
Igniter
Fan motor
Hot water
Cold water
Inlet
Thermistor
Air-fuel ratio rod
Flame rod
Surge box
PCB GFI
AC120V
Transformer
120 VAC

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6. Wiring diagram
W: WHITE R: RED
BK: BLACK
P: PURPLE
LB:LIGHT BLUE
BL: BLUE
G: GREEN
Y: YELLOW
O: ORANGE
BR:BROWN
GY:GRAY
J
H1
H2
E1
E3
E2
C1
C2
G
B
F
D1
D2
I
A2
A
A1
C
L
C
C
C
K
A3
9007603005
Inlet
thermistor
Output
thermistor
Mixing
thermistor
BK
BK
BK
H i-
li mit
sw itch
Air-fuel
ratio rod
Ground
Flame rod
MV
SV3
SV1
SV2
FM
Igniter rod
IG
RYGW
BK
BR
ROYGW
BK
BL
Water
Control
valve
O.H.C.F
BL
BL B L
BL
Y
G
O
R
BL
YOW
P P
P
P
Gas
Propor-
tional
Valve
Flow
Sensor
W
R
BKW
R
WR
BK
RW
BL
BL
BL
LB
G
O
R
Paren
t
W
W
BK
BK BL
BL
R
R
Remote
controller
W
BK
Heater
Thermostat
Heater
BK
BK
G
W
BK
Trans-
former
Ground
BR
BR
120 VAC
G
Ground
BK
WW
BK
BR
BR
Surge
box
WBK
Heater
1 2 3 4 5 6
OFF
7 8
GFI
12 3 4 5 6
OFF
7 8
BK
W
Pump
Heater
2
1
GY
GY
P
P
O
O
3
4
7 Seg LED
Left bank of
dipswitches
Right bank of
dipswitches
MAX button
MIN button
Increase button
Decrease button
Error call bu tton
Burning lamp
Number display button

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7. Wiring diagram check points for diagnosis
Check-
point
Parts and Description
Color of wires Normal Range
A, A1
100 V Power supply White –Black (A)
Brown –Brown (A1) 90 to 110 VAC
A2,A3
120 V Power supply Black - White 108 to 132 VAC
B Igniter Purple –Purple 90 to 110 VAC
Light blue - blue at COM (MV)
78 to 100 VDC (during operation)
/ 0.9 to 1.3kΩ
Green - blue at COM (SV1) 78 to 100 VDC (during operation)
/ 1.3 to 1.9kΩ
Orange - blue at COM (SV2) 78 to 100 VDC (during operation)
/ 1.3 to 1.9kΩ
C Gas valves
Red - blue at COM (SV3) 78 to 100 VDC (during operation)
/ 0.9 to 1.7kΩ
C1 Hi-Limit switch Blue - Blue Less than 1 VDC and less than 1 Ω
C2 Overheat cutoff fuse Blue - Blue Less than 1 VDC and less than 1 Ω
White - White 15 VDC
D1 Easy-link connectors Red –Red
Blue –Blue
15 VDC
(during Easy-link operation)
D2 Multi-unit link
connectors
Purple- Purple
Orange -Orange
15 VDC
(during Multi-unit operation)
E1 Mixing thermistor Black - Black
E2 Output thermistor Black - Black
E3 Inlet thermistor Black - Black
See table on p.12
F Remote controller Black - White 11 to 25 VDC
Red - Blue 110 to 160 VDC
Yellow - Blue 13 to 17 VDC
G Fan motor
Orange - Blue 2 to 6.5 VDC
H1 Gas proportional valve
White - red
1 to 15 VDC (during operation)
and
20 to 40 Ω

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Check-
point
Parts and Description Color of wires Normal Range
Red - Black 4 to 5.5 VDC
H2 Flow sensor
White(+) –Black(GND)
1 to 4 VDC (1,200 Pulse/min)
Air-fuel ratio rod
Yellow –AFR rod
(Between AFR rod and
the computer board)
More than 0.5 μA
(during operation)
I
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 to 16 VDC
ON: 12.5 to 16 VDC
OFF: 0 to 1 VDC
1 VDC Less ( 0°C position)
K Pump connector White - Black Less than 1.3 Ω
L Heater Black –Black 90 to 110 VAC

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8. Resistance values of the temperature 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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9. Operational flow chart
Power supply ON
Operation SW ON
FAV&BV open
Pre-check
NORMAL?
Faucet opens
Water Flow
Above 0.5GPM?
FM speed
(Below
1,000rpm?)
Fan moter start
operation
Flame rod
detects Below
DC0.15 A?
Igniter ON
Hi-limit
Normal?
OHCF
Normal?
MV ON
SV2 ON
GPV ON
Flame rod
detects Above
DC1.0 A?
Burning lamp ON
Igniter OFF
Proportional control
BTU
change over
point?
SV1 SV3 ON
Below water
heat capability?
FAV OPEN
Safety devices
sensed
abnormal condition
FAV CLOSE
SV1 SV3 OFF
False Dipswitch
settings
InTH failure
PCB failure
MV circuit failure
031 blink
321 blink
701 blink
510 blink
611 blink
Fan motor stop
operation
721 blinkFalse flame
Igniter OFF
Reignition
Success?
OuTH OPEN
or SHORT
Fan motor
fault
MV OFF
SV2 OFF
GPV OFF
SV1 SV3 OFF
Fan motor
stop operation
Faucet closes
Flow sensor OFF
Remove cause
Opeartion lamp OFF
Operation stop
YES
NO
YES
NO
NO
YES
YES
NO
(20sec later)
YES
NO
NO
YES
YES
NO
YES
NO
(5sec later)
(3sec later)
YES
YES
NO
YES
NO
(20sec later)
YES
NO
NO
NO
YES
FM speed
(Above
1,000rpm?)
Below
Max flow rate
restriction?
111 blink
121 blink
611 blink311 blink
OuTH failure 311 blink
MiTH failure 331 blink
Flame
blows out
OHCF melted
(above 430 F)
AFR rod failure Abnormal
burning
121 blink121 blink991 blink391 blink
BV modulates
Flow&temp
321 blink
InTH OPEN
or SHORT
331 blink
MiTH OPEN
or SHORT
FAV ; Flow Adjustment Valve
B V ; Bypass Valve
F M ; Fan Motor
OHCF; Over Heat Cut-off Fuse
M V ; Main gas Valve
SV1 ; Solenoid Valve 1 (See the section 6)
SV2 ; Solenoid Valve 2 (See the section 6)
SV3 ; Solenoid Valve 3 (See the section 6)
GPV ; Gas Proportional Valve
InTH; Inlet thermistor
OuTH; Output thermistor
MiTH; Mixing thermistor
PCB ; Print Circuit board
(Computer board)
AFR ; Air Fuel Ratio rod
SV circuit failure 551 blink
661 blink
Fault of Flow
adjustment function
in Water control
Valve
Fault of Bypass
function in Water
control Valve
651 blink

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10. Component specifications
10-1.
Burners……………………..…………………………………………….………………………....……….
15
10-2.
Gas manifold…………….…………………………..………………………………………………….....
16
10-3.
Fan motor……………………………………………………………………….………………………...…
17
10-4.
Gas valve assembly……………………………………….……………………………………….…….
18
10-5.
Flame rod………………………………………………………….…………………………………………
19
10-6.
AFR rod……………………………………………………………………………..…………………………
20
10-7.
Heat exchanger…………………………………………………………….....………………….………
21
10-8.
Flow sensor………………………………………………………………………………………………….
22
10-9.
Water Control valve………………………………...………………………………………………..…
23
10-10.
Thermistors………………………………..……………………………………..…………………………
25
10-11.
Hi-limit switch………………………….…………………………………………………………..………
26
10-12.
Overheat cutoff fuse..……………………………………………………………………………..……
27
10-13.
Freeze protection heaters….……….………………………………………………………………..
28
10-14.
Computer board…………………………………………………………………………………………..
29
10-15.
Transformer…………………………………………………………….………….……………………….
30
10-16.
GFI…………………………………………………………………………………................................
31
10-17.
Igniter……………………………………………………………………………….............................
32
10-18.
Freeze protection thermostat……………………………………………………....................
33
10-19.
Surge box……..…………………………………………………………………............................. 34

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10-1. Burners
Unit Part ##101 AOS Part #319143-299
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 event
1. Unable to initialize/sustain combustion.
2. Dust or soot deposit on the burner surface.
3. Cracks of 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 V isual inspection: excessive dust deposit on the burner surface and/or
unstable flame conditions during operation.
Color / Number of wires N/A
9-5/8" (24 5 m m)
1-3/4" (4 4 m m) 33T
"33T" mark
The burner damper is not
included in 319143-299.
Burner damper (#111 / 319143-298)
7-1/2" (190mm)5-1/4" (132mm)
10-3/4" (273mm)

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10-2. Gas manifold
Unit Part ##120 AOS Part #319143-305 (LP model)
319143-306 (NA model)
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 (20
nozzles) and the other for air-rich burners (19 nozzles)
2. There are 3 zones within the manifold, to ensure efficient combustion
operation.
Failure event
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 air-rich burners
Nozzles for gas-rich burners
319143-305 (for LP model) and 319143-306
(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 has the “33T”mark on the
manifold plate.
10-7/ 8" (2 77 mm)
7-7/8 " (20 3 mm)
33T
"33T" mark

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10-3. Fan motor
Unit Part ##115 AOS Part #319143-043
Checkpoint G
Function To provide combustion air into the combustion chamber and to exhaust
flue gas.
Failure event
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.
Red-Blue 110 to 160 VDC (Input)
Yellow-Blue 13 to 17 VDC (Input)
Orange-Blue 2.0 to 6.5 VDC (Input)
Color / Number of wires
White-Blue Verify the fan motor speed using the Diagnostics Mode of
the temperature remote controller. See Section 12-1 for
details.
Fan damper (#116 / 319143-282)
PWN turbo fan motor
6-1/2" (165.5mm)
3-3/4"(95.15mm)
Opening 2-1/8"( 54mm)
The fan damper
is not included in
319143
-
043.
1-3/4"
( 46mm
)
46

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10-4. Gas valve assembly
Unit Part ##120 AOS Part #319143-305 (LP model)
319143-306 (NA model)
Checkpoint
C,H1
Opens and closes the gas pathways of the water heater (main and solenoid
gas valves)
Function
Modulates the gas flow from the gas inlet (proportional gas valve)
Failure event
1. Gas leak from the valves.
2. Unable to open /close (main and solenoid gas valves)
3. Unable to modulate the gas flow (proportional gas valve)
Effects on the water
heater if valves fails
1. Gas leak from the unit.
2. Excess carbon monoxide emissions. / No flames.
3. Lack of water temperature control.
Error codes when the
valves fails 111 121 510 701
Diagnostic
1. Visual inspection: connection / 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.
Blue -Light blue 78 to 100 VDC (during operation) / 0.9 to 1.3 kΩ
Blue -Green 78 to 100 VDC (during operation) / 1.3 to 1.9 kΩ
Blue -Orange 78 to 100 VDC (during operation) / 1.3 to 1.9 kΩ
Blue -Red 78 to 100 VDC (during operation) / 0.9 to 1.7 kΩ
Color / Number of wires
White –Red
(Proportional valve) 1.0 to 15 VDC (during operation) / 20 to 40 Ω
4-1/2"(114mm) 4-1/2(119mm)
319143-305 (for LP model) and 319143-306 (for NA
model) is an assembly of the gas manifold with gas valve
assembly. For safety reasons, these assemblies should
be installed in the unit as a whole set. The diagram
below shows the gas valve assembly.

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CONFIDENTIAL
10-5. Flame rod
Unit Part ##106 AOS Part #319143-035
Checkpoint I
Function To detect flames while the water heater is in operation.
Failure event 1. Unable to detect flames when flames actually do occur
2. Detecting a false flame when no flames actually occur
Effects on the water
heater if flame rod fails
1. The water heater stops operating. The "111" and/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 inspection: connection / breakage of wires or soot buildup on rod.
2. Check amperes: proper range of values shown below.
Color / Number of wires
Orange(17) - Flame rod
(Between the flame rod and
the computer board)
(During operation)
More than DC 1 μA
The flame rod is assembled with the AFR rod.
Leads to computer board
Detecting elements of the flame rod
AFR Rod
Flame rod
3/4 " (1 7.5 m m)
1/4 " (7 .5 mm)
1/2 " (1 2mm )
1-1 /8" (29.3 m m)
1-3/4" (44mm)

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10-6. AFR rod
Unit Part ##106 AOS Part #319143-035
Checkpoint I
Function
-Checks flame conditions during combustion.
-When AFR rod detects unexpected flame conditions, the the computer of
the water heater makes adjustments in the fan motor speed to compensate.
Failure event 1. Unable to detect flames when flames actually do occur
2. Detecting a false flame when no flames actually occur
Effects on the water
heater if AFR rod fails
1. The water heater will not initiate the ignition process. The "721" error
code will display.
2. The fan motor speed cannot be modulated properly under abnormal flame
conditions, which can result in excessive CO emission.
Error codes when the
AFR rod fails 101 391 991
Diagnostic 1. Visual inspection: connection / braking of wires, soot on it.
2. Check voltages: proper range of values are shown below.
Color / Number of wires
Yellow(8) - AFR rod
(Between the flame rod and
the computer board)
(During operation)
More than DC 0.5 μA
The AFR rod is assembled with the flame rod.
Leads to computer board
Detecting elements (AFR and flame rods)
AFR Rod
Flame rod
3/4" (17.5mm)
1/ 4" (7.5mm)
1/ 2" ( 12m m)
1 -1 /8" (2 9.3 m m)
1-3/4" (44mm)