Noritz NH-2001- DV User manual

1
NORITZ America Corporation
GAS-FIRED DIRECT VENT BOILER
NH-2001- DV
NH-1501- DV
Service Manual
•Refer to this manual whenever performing service or
maintenance on this appliance.
•This manual will be used for service technician training
seminars.
•The specifications and descriptions in this manual may
be changed without prior notice.
•For further assistance, contact Noritz Technical Support
at 1-866-766-7489.
Do not short circuit any safety
device on this appliance
Rev: January, 2007
Contents
Important Safety Information ....................................................................................................2
1. Product Features ................................................................................................................ 3
2. Specifications/Performance Table ...................................................................................... 4
3. Dimensions ......................................................................................................................... 6
4. Components ....................................................................................................................... 7
5. Operating Principle ............................................................................................................. 9
6. Operation Flow Chart ......................................................................................................... 11
7. Wiring Diagram ................................................................................................................... 13
8. Troubleshooting .................................................................................................................. 15
•Error Codes and Checkpoints ......................................................................................... 15
• Checkpoints .................................................................................................................... 16
•Error Descriptions and How to Reset.............................................................................. 17
•Operation Panel (Remote Controller) ............................................................................. 20
•Displaying Maintenance Monitors on the Operation Panel (Remote Controller) ............ 20
•Maintenance Monitor List ................................................................................................ 21
• Circuit Board Replacement ............................................................................................. 22
• When Changing the Fan Motor ....................................................................................... 23
• Gas Line Requirements .................................................................................................. 24
• Gas Line Sizing Charts ................................................................................................... 25
• Manifold Gas Pressure Adjustment ................................................................................ 26
•Periodic Inspection.......................................................................................................... 27
•Changing Boiler Settings ................................................................................................ 29
• Installations at Elevations Above 2,000 ft. ..................................................................... 30
•Emergency operation procedure..................................................................................... 30
9. Installation Check ............................................................................................................... 31
WS-06-9018

2
Important Safety Information
To prevent damage to property and injury to the user, the icons below warn of
varying levels of risk.
CAUTION
WARNING
Ignoring this indication will cause an immediate danger of death or
serious injury.
Ignoring this indication may result in death or serious injury.
Prohibited.
1. Safety Tips for Service
•Wear the appropriate clothing and protective gear:
In order to prevent injury or accident, wear a protective helmet, safety boots and a lifting
belt whenever necessary.
CAUTION
• Use only the appropriate tools and parts:
WARNING
Only use replacement parts manufactured by Noritz for this model as listed in the
Parts List for service on this unit. Use appropriate tools.
•Modification of the unit is prohibited:
Do not attempt to modify or alter the unit. This will cause a fire hazard and a risk of
electrical shock.
•When servicing:
WARNING
Disconnect the power supply during maintenance and repairs to reduce the risk of
electric shock. If it is necessary to have the electricity connected during repairs, use
extreme caution not to touch parts that may cause a shock.
• Do not short circuit any safety device on this appliance:
If a safety device is not functioning properly, replace the part. Do not under any
circumstances short circuit the part.
•Exhaust and gas leakage caution:
WARNING
Always check for leaks when installing or modifying the exhaust vent or gas piping.
2. Post-Service Checks
•Check parts for leaks:
CAUTION
Confirm that there are no gas, water, or exhaust leaks regardless of whether the
service performed could have caused them.
Check that the flue collar and vent pipe are installed correctly and that they are in
good condition. Confirm that there are no gas, water or exhaust leaks regardless of
whether the service performed could have caused them.
•Check for combustibles:
CAUTION
After service or maintenance is completed, check that there are no combustibles in
the vicinity of the unit.
•Check insulation resistance:
WARNING
After service or maintenance is completed, measure the resistance between the elec-
trical wires and ground. If it is less than 10M , there is a risk of electrical shock.
•Properly reconnect the power supply:
WARNING
Confirm that the power supply has been reconnected properly after service or main-
tenance is completed. Also confirm that there is no dust or other obstacles that might
cause an electric shock or a fire hazard.

3
1. Product Features
1. An external controller is unnecessary in a basic system.
An external zone controller is unnecessary for the indirect tank (PRIORITY1) and heating systems
(PRIORITY 2) which do not use multiple zones.
The boiler has two T-T connections and two circulator output terminals.
2. Dual temperature control
The hot water supply temperature can be set between 140°F-180°F.
It can be customized for PRIORITY1 and PRIORITY2.
3. Flow switch activation
The boiler is equipped with a water flow switch which prevents the boiler from firing when little or no
flow is circulating through the heat exchanger.
Should the circulator, zone valve, etc. fail, the flow switch will also prevent damage to the heat
exchanger.
4. Freeze prevention
Freezing within the boiler caused by a drop in temperature at the installation site or a backflow of
cold air from the outdoors is prevented with the on-board freeze prevention control.
*Refer to the "Installation and Instruction Manual" for limitations on this control.

4
2. Specifications/Performance Table
Specification
NH-1501-DV
Indoor Wall Hanging
Direct Vent / Sealed Combustion
Closed type hot-water circulation method
Direct Ignition
15-150 psi
30 psi
24.2"(Height) x 18.3"(Width) x 9.4"(Depth)
65.3 lbs.
0.4 Gallon
1 "
1"
3/4"
120 VAC (60Hz)
NG : 97W LP : 111W
Zincified Steel Plate/Polyester Coating
Stainless Steel
Copper Sheeting, Copper Tubing
Flame Rod, Thermal Fuse, Lightning Protection Device (ZNR), Overheat
Prevention Device, Freezing Prevention Device, Fan Rotation Detector,
Boil-dry Safety Device, Boil-dry Protection Device, Overcurrent Protection Device
Pressure & Temperature Gauge, Safety Relief Valve (valve, fitting, and gasket),
Anchoring Screws, Terminals
Performance
Item
Model Name
Type
Ignition
Operating Pressure
Safety valve setting pressure
Dimensions
Weight
Water Holding Capacity
Accessories
Installation
Air Supply/Exhaust
Heating method
Connection Sizes
Power Supply
Materials
Supply
Return
Gas Inlet
Supply
Consumption (*)
Casing
Flue Collar
Heat Exchanger
Safety Devices
Item
Gas
Consumption
Standard output
Temperature Settings
NG
LP
140-170°F (In 5°F intervals), 176, 180°F (9 Options)
NH-2001-DV
199,900 btuh
NH-1501-DV
150,000 btuh
4-17 GPM (bypass minimum-flow rate: 2.5GPM)Amount of boiler water used
NH-2001-DV
55,500 btuh 55,500 btuh
Maximum Performance
Minimum Performance
Maximum Performance
Minimum Performance
199,900 btuh 150,000 btuh
55,500 btuh 55,500 btuh
60-80°C (In 5°C intervals), 83°C (6 Options)
45,500-163,100 btuh 45,500-122,400 btuh
Fahrenheit
Centigrade
NG : 93W LP : 93W
AFUE NG
LP
82.7% 83.0%
83.0% 82.8%
*The values listed are for the boiler only.
The maximum current draw by the unit with 2 pumps connected will be 6 amperes or less.

5
Heating load - Temperature Specification
Pressure Loss Characteristics
The total flow rate of the heating circuit should be no less than 4 gpm (15 L/min.) and no greater
than 17 gpm (65 L/min.).
Flow rate (GPM)
0 3.8 7.6 11.4 15.2 19.0 22.8 26.6 30.4 34.2 38.0 41.8 45.6 49.4 53.2 57.0 60.8 64.6
Flow rate (L/min)
Setting Temp. +13°F
Note) Maximum temperature is 188°F (87°C)
Proportional control
Setting Temp. Setting Temp.
Temperature
(approximately)
Setting Temp. -18°F
Setting Temp. +7°C
Setting Temp. -10°C
NH-1501-DV
NH-2001-DV
45,500 btu/h
45,500 btu/h
122,400 btu/h
163,100 btu/h
(approximately)
Heating load

6
3. Dimensions
WIRING THROUGHWAYS
WATER SUPPLY(1")
GAS INLET(3/4")
WATER RETURN(1")
"14.2
"10.6
"8.9
"2.4
"6.8
"6.8
"5
"3.2
"6.4
"5.8
"4.3
"4.6
(WATER DRAIN VALVE)
"26.2
"
6.7
"
5.5
"
3.9
"
2.8
"
1.4
"
6.7
"
5.5
"
3.9
"
2.8
"
1.4
17.7"
(WATER FILTER)
BOTTOM OF CASE
PRESSURE RELIEF VALVE
WATER DRAIN VALVE
WIRING THROUGHWAYS
WATER SUPPLY
GAS INLET
WATER RETURN
BOTTOM OF CASE
"7
"5.7
"0.4
"9.4
"3.7
"0.4
"1.6
OPERATION
PANEL
AIR INLET FLUE COLLAR
9.1"
"4
"24.2
18.3"
"4
5.9"
1.7"
"2.2 "3.4
"2.6
(VIEW FROM TOP)

7
4. Components
Transformer
Heat Exchanger
Circuit Board SC
Circuit Board
Heat Exchanger Thermistor
Water Return Thermistor
Water Supply Thermistor
Water Flow Switch
Gas Valve Mechanism
Air Inlet Exhaust Flue
Air Inlet Thermistor
Flame Rod
Thermal Fuse
Ignition Electrode
Manifold
Safety Relief Valve
High Limit Switch
Igniter
Fan Motor
Junction Box
(Inlet Filter)
Drain Plug Water Drain Plug
Gas Inlet
Water Supply
Water Return

8
Operation Panel (RC-7648M)
For changing the set
temperature and
performing various
settings.
Setting Buttons
Temperature Setting
(Ex.: 180°F)
A number will flash if
a failure occurs.
Burner On Indicator
When burning, the indicator is lit.
•The indicator will flash when
the temperature of
PRIORITY 1 (Indirect tank
use) is displayed.
•The indicator is lit during
PRIORITY 1 (Indirect tank
use) operation.
PRIORITY 1 Indicator
Error Code
Power On/Off Button
For turning the
boiler on and off.
For setting the temperature
of PRIORITY 1.
PRIORITY 1 Button
For setting the temperature
of PRIORITY 2.
PRIORITY 2 Button
For changing the maximum
temperature setting of
PRIORITY 1.
Maximum Temperature
Setting Button
* Before use, remove the protective sheet from the remote controller surface.
• The indicator will flash
when the temperature
of PRIORITY 2 (Heating
use) is displayed.
•The indicator is lit
during PRIORITY 2
( Heating use )
operation.
PRIORITY 2 Indicator

9
5. Operating Principle
T-T connection
Contact for Lamp
Circulator outputs,
Air inlet thermistor
Controller
SC
Controller
Rotational
frequency sensor
Fan motor
Air supply
AC 120V
Transformer
Gas solenoid valve-2
Gas solenoid valve-1
Gas solenoid valve-3
Water supply thermistor
Drain plug
Supply Gas Return
Inlet filter
Water drain plug
Water flow
switch
Primary gas
valve
Gas proportioning
valve
Burner
Flame rod
Ignition plug
Igniter
Over heat prevention
device (Thermal fuse)
Water return thermistor
Heat exchanger
thermistor
Exhaust
High limit switch
Safety relief
valve

10
< How to Use, NH-2001-DV / NH-1501-DV >
1. Normal Operation (Priority1 or Priority2)
1. Turn on the power by pressing the "POWER" button on the operation panel (remote controller).
(Power indicator lit.)
2. When the Operation switch of the "Indirect tank" or "Room thermostat" is turned ON (Priority1 or Priority2 calls for
heat), the boiler supplies power to the Priority1 or Priority2 circulator.
3. When the water flow switch is ON and water supply thermistor detection temperature is lower than combustion
start temperature, the fan will initiate and pre-purge any residual combustible gas in the combustion chamber,
and then the igniter begins to spark. Finally, the gas valves open, and burner is ignited by the spark.
4. When the flame rod detects a flame, the igniter stops sparking.
5. The computer will then control the gas and fan to maintain the supply temperature set on the operation panel
(According to "Priority1 temperature setting" or "Priority2 temperature setting").
The temperature can be adjusted using the "Priority1" button or "Priority2" button on the operation panel.
* When "Priority1" and "Priority2" both call for heat, the boiler gives priority to the "Priority1" circuit.
* When the heating load is too small, the burner is controlled ON/OFF.
6. When the Operation switch of the "Indirect tank" or "Room thermostat" is turned OFF (Priority1 or Priority2 no
longer calls for heat), the gas valve will close and the burner flame will go out. After the post purge removes
residual gas from the combustion chamber and post circulation removes the residual heat from the heat
exchanger, the appliance stops.
7. When the boiler is not being used for an extended period of time, turn off the power by pressing the "POWER"
button on the operation panel. (Power indicator OFF)
2. Error Codes
If the flame rod does not detect a flame, or if the high limit switch has been triggered, the gas valve will close, the
flame will go out, and an error code will flash on the operation panel. In order to reset the boiler and remove the
error code, turn the power off by pressing the "POWER" button on the operation panel, and then press it again to
turn the boiler back on. If the problem requires service ( the thermal fuse is triggered, etc.) the gas valves will stay
closed and resetting the appliance will not eliminate the error code. If this is the case, the boiler must be serviced
(repaired) before it will work again.
3. Miscellaneous
If the boiler will not be used for a long period of time, turn off the power, and close the manual gas valves on the
supply line.

11
6. Operation Flow Chart
(Passage of 20
seconds from .)
Priority1 & 2
(Passage of 25 seconds from .)
(Passage of 20
seconds from .)
b
A
A
a
a
ab
b
(Passage of 20
seconds from .)
a
Gas solenoid valve-3 closes
YES
Gas solenoid valve-3 closes
Gas solenoid valve-3 closes
Gas solenoid valve-2 closes
YES
Heating load
less than 71,000btu/h
NO
YES
*2
*2
*2
*2
Overheat Prevention
(363 ° F or more)
Overheat Prevention Device
NO
YES
Priority2 does not call for
heat
Combustion stop IH
9
I
H
*2
Priority1 circulator OFF
Priority2 circulator OFF
NO
YES
Passage of 20 seconds
from the circulator ON
2
19
Priority2 circulator ON
Priority1 circulator ON
YES
NO
Connect power or
the last circulation
Passage of 360 hours from
Priority2 circulator OFF
Priority1 circulator OFF
NO
YES
(2.5 GPM or more)
Water flow switch ON
719
643
Priority2 circulator abnormality
Water flow switch OFF failure
NO
(2.5 GPM or more)
Water flow switch ON
(after 5 sec.)
YES
(after
60 sec.)
203
17
High limit switch
triggered
Priority2 circulator ON
19
C
B
Initial check
D
C
GF
Priority2 operation
G
F
Fan motor OFF
Priority1 circulator OFF
Priority2 indicator (green) OFF
YES
Priority2 does not call for
heat
NO
Priority2 indicator (green) lit
Priority1 indicator (orange) OFF
Gas solenoid valve-2 closes
Burner ON indicator (red) OFF
Primary gas valve closes
Gas proportioning valve closes
Gas solenoid valve-1 closes
Priority1 does not call for heat
E
D
Combustion control
Change to the priority2
temperature setting
EA
Priority1 operation
A
NO
YES
Priority1 does not call for
heat
Priority2 calls for heat
Gas solenoid valve-1 closes
Gas solenoid valve-2 closes
Gas proportioning valve closes
Burner ON indicator (red) OFF
Primary gas valve closes
903
Combustion
abnormality
143
1
Overheat Prevention
Device (Thermal Fuse)
triggered (363
° F or more)
333
5
Heat exchanger
thermistor
Open or shorted
4
323
Water supply
thermistor
Open or shorted
8 18
3
313
Water return
thermistor
Open or shorted
72
253
Water flow switch
ON failure
163
Water supply
temperature
does not stabilize
613
Burner ON indicator (red) OFF
Primary gas valve closes
Gas solenoid valve-1 closes
Gas proportioning valve closes
Gas solenoid valve-2 closes
*1
Fan speed
abnormality
Burner ON indicator (red) OFF
15
Flame rod detects no flame
(0.5 µA or less)
E
NO Safety device
triggered
NO Water supply
thermistor < combustion
YES
stop temperature
13
Gas solenoid valve-2 opens
NO
115,000btu/h or more
Heating load
Gas solenoid valve-3 closes
1st,4th,7th:after 5 sec.
others:after 2 sec.
Igniter stops sparking
Primary gas valve closes
Gas solenoid valve-1 closes
Gas proportioning valve closes
Gas solenoid valve-2 closes
Fan motor OFF
High limit
switch
Flame rod
Ignition
failure
17
203
123
113
NO (3rd)
High limit switch
is normal
YES
NO
YES
Extinction
(5 times or less)
NO
YES
Re-ignition
(8 times or less)
Proportional control (gas,fan)
16
Gas solenoid valve-2 closes
Gas solenoid valve-3 opens
13
Gas solenoid valve-2 opens
Igniter stops sparking
Burner ON indicator (red) lit
613
15
YES
NO
Flame rod detects
(1 µA or more)
Gas proportioning valve opens
Gas solenoid valve-1 opens
14
12
11
Primary gas valve opens
10
Igniter sparks
Fan motor OFF
9
(after 60
sec.)
Fan speed
start temperature
Water supply
thermistor combustion
Water flow switch ON
(2.5 GPM or more)
NO
YES
8
Fan motor ON
NO
YES
Priority1 circulator abnormality
Water flow switch OFF failure
Priority1, 2 circulator OFF
1
2
6
5
4
3
1
B
633
YES
(after 60
sec.)
NO
(after 5 sec.)
Priority1 circulator ON
Heat exchanger thermistor
Open or Shorted
Water supply thermistor
Open or Shorted
Gas valve drive circuit abnormality
Circuit board abnormality
Flame rod circuit abnormality
(1µA or more)
Water return thermistor
Open or Shorted
(Thermal Fuse) triggered
do not call for heat
Power button OFF
Error code stops flashing
713
703
723
333
323
313
143
YES
NO
normal
Initial check
Priority1 indicator (orange) lit
Priority1 calls for heat
143
NO
YES
(Less than 363 ° F)
Device (Thermal Fuse) normal
Disconnect power
Fix problem
The boiler will continue
to operate with the error code
blinking on the operation
panel (remote controller).
Warning indication
903
993
YES
NO
Self-diagnosis
possible
Normal combustion
Warning
indication
Warning
indication
103
903
YES
possible
Self-diagnosis
Normal combustion NO
Maximum output limited
YES
NO
Use for less than
10 years
YES
NO
possible
Normal combustion
Self-diagnosis
Power indicator (green) lit
Power button ON
Connect power
*2 Time is managed respectively "Priority1
and 2". Only the circulator where timer
is up operate.
*1 When the present fan speed is 500 rpm more or less than the target speed.
(target 200rpm)
Circulator lock
prevention control
Shutdown procedure
Priority2 operation
Priority1
operation

12
B
B
YES
B
B
B
B
Priority1 & 2 Freeze
prevention control data clear
Priority1 & 2 Freeze
prevention control data clear Priority2
Freeze prevention control
incomplete
Priority1
Freeze prevention control
incomplete
Priority1
Freeze prevention control
disabled
Priority2
Freeze prevention control
disabled
control completion
Priority2 Freeze prevention
control completion
D
C
completion
Freeze prevention control
Priority2
Priority2
Freeze prevention control
disabled
completion
Freeze prevention control
Priority1
Priority1
Freeze prevention control
disabled
D
D
CPriority1 Freeze prevention
control completion
control disabled
control disabled
control completion
C
Priority2
Freeze prevention control
completion
Priority2
Freeze prevention control
disabled
Priority1
Freeze prevention control
completion
Priority1
Freeze prevention control
disabled
Priority1
Freeze prevention control
permission
Priority2
*5
20
Warning
indication
303
NO
YES
Air inlet thermistor
normal
NO
NO
NO
HI
YES
50° F (10° C ) or more
Water return thermistor
Combustion stop
86° F (30° C ) or more
YES
Water supply thermistor
NO
NO
YES
YES
Priority1 circulator OFF
Priority1 circulator OFF
IH
YES
Combustion stop
NO
NO
NO
2
YES
Priority1 circulator ON
NO
NO
YES
YES
Priority1 circulator OFF
NO Water flow switch ON
(2.5 GPM or more)
YES
Priority1 circulator ON
Less than 5 minutes from
ED
NO
YES
NO
Combustion control
YES
(after 50 sec.)
Priority1 circulator ON
YES
Less than 5 minutes from
(after 60
sec.)
Priority2 circulator OFF
YES
NO
Priority2 circulator OFF
NO
YES
HI
Combustion stop
50°F (10° C ) or more
Water return thermistor
YES
NO
NO
86°F (30° C ) or more
Water supply thermistor
YES
IHCombustion stop
YES
NO
YES
NO
NO
YES
Less than 5 minutes from
Priority2 circulator ON
Priority2 Freeze prevention
Priority2 circulator OFF
ED
Combustion control
(after 50 sec.)
NO
(after
60 sec.)
(2.5 GPM or more)
YES
Water flow switch ON
NO
NO
YES
YES
NO
YES
Priority2 circulator ON
Less than 5 minutes from
NO
Freeze prevention control
permission
YES
YES
NO
YES Water return thermistor
NO
YES
34°F (1°C) or less
Water supply thermistor
34° F (1° C ) or less
Heat exchanger thermistor
34°F (1°C) or less
NO
NO
Heat exchanger thermistor
YES
41°
F (5° C ) or less
YES
Water return thermistor
41°
F (5° C ) or less
NO
Water supply thermistor
YES
41° F (5° C ) or less
NO
Air inlet thermistor
YES
19 Priority2 circulator ON
37° F (3° C ) or less
Display OFF
Priority1 indicator (orange) OFF
NO
YES
Passage of 5 minutes from
water flow switch OFF
of
Display lit
Priority1 circulator OFF
on
Display lit
NO
(after 2 sec.)
(2.5 GPM or more)
YES
Water flow switch ON
(after 2 sec.)
2Priority1 circulator ON
of
P
Display lit
Display flashing
Priority1 indicator
(orange) flashing
*3
*4
Priority1 button ON
NO
YES
Passage of 4 hours from
this procedure start
*3 This flow chart has described priority1 circulator manual operation.
Please press the "Priority2 button", when you want to operate Priority2 circulator.
*4 Press and hold the Priority 1 or 2 button for at least 5 seconds.
*5 The circulator will be turned off when either the Power button is turned "ON" or
the Priority 1 or 2 button is held in for at least 5 seconds.
When "Priority1" and "Priority2" both call for heat,
this appliance gives priority to the "Priority1" circuit.
Freeze prevention control
Manual
circulator operation
procedure
Fahrenheit select
67
72
77
82
87
50
55
60
65
70
60
65
70
75
80
83 8773
122
127
132
136
141
147
152
158
Centigrade select
140
145
150
155
160
165
170
176
152
158
163
167
172
177
183
188
188163180
Combustion
stop temperature
Combustion
start temperature
Temperature setting
(Control temperature)
Control temperature
Priority of control
Priority2 Freeze prevention
Priority1 Freeze prevention
Priority1 Freeze prevention

13
7. Wiring Diagram
R : Red
RESISTANCE
BKBK
W
W
W
W
W
W
W
W
W
W
W
W
V
W
R
W
BLBK
BL
BK
Factory
Use Only
V
W
W
R
W
V
R
W
V
W
W
R
BR
BR
O
O
BL
BK
BL
BK
BR
BR
O
OBK
BLBL
BK
W
BK
W
BL
WW
Factory Use Only
BL
BL
BL
BL
V
V
FAN SPEED CORRECTOR
AIR FLOW SWITCH
OO
O
EMERGENCY OPERATION
SWITCH
YY
Y
V
V
BK W
WRW
OOBRBRWBKW
SYSTEM
CONTROL
CIRCUIT
BOARD
G
EARTH
V
BK
W
W
W
W
WW
W
W
EARTH
G
W
W
V
BR O
<CN211>
<CN54>
<CN89C>
<CN33>
W
R
BL
BL
BR
O
JUNKTION
BOX
BL
W
W
BL
BK
W
BL
BL
BKBK
WATER FLOW
SWITCH
BK
W
W
<CN70>
<CN75>
BK
WWWW
<CN63>
W
ROYW
<CN102>
BL
Minimum Manifold Pressure
Set Button
Maximum Manifold Pressure
Set Button
Increase Button
Manifold Gas Pressure
Decrease Button
Manifold Gas Pressure
GAS VALVE
UNIT
BK
BK
O
GY
GY
R
BL
R
BL
W
W
BK
BL
GY
W
O
O
BL
R
<CN184>
BK
BL
W
GY
O
MAIN
CIRCUIT
BOARD
O
BL
BK W GY
WBK
GW
<CN10>
RBLBL
BL BL
<CN89A>
BLW
<CN92>
<CN102>
G
OWW Y
<CN104>
POWER
CIRCUIT
BOARD
BL
W
BK
EARTH
<CN101>
BL
BL
<CN89>
R
BL
<CN38>
WW
WW
W
WW
WW
W
WW
BK W
WW
BK W
WATER RETURN
THERMISTOR
HEAT
EXCHANGER
THERMISTOR
WATER SUPPLY
THERMISTOR
AIR INLET
THERMISTOR
WIRING DIAGRAM
BL
BL
<CN78>
<CN27>
YBLRBR
BR
R
Y
BL
BR
R
Y
BL
BL
BL
BL
BL
BL
BL
Y(FG)
BL(GND)
R(Vcc)
BR(Vdc)
THERMAL FUSE
FLAME ROD
FAN MOTOR
REMOTE CONTROLLER
W
BK
W
W
IGNITER
BK
W
ELECTRODE
HIGH-LIMIT
SWITCH
COLOR CODING
G : Green
EARTH
RC-7648M
<CN1>
BK
BL
TRANSFORMER
Y : Yellow
BL : Blue
O : Orange
GY : Gray
BR : Brown
W : White
1
2
1
2
1
2
1
1
1
11
2
3
4
1
2
2
1
2
1
2
1
3
1
1234 5678
2
1
2
3
4
3
1
1
2
23456789
1234561234
1
12341234123
1
1
2
1
2
3
4
1
2
3
4
23
45
1234
234
5678
56
1
1
1
2
3
4
2
3
4
5
6
789
1
2
3
4
1
1
2
3
4
1
2
3
4
1
2
3
4
2
3
1
11
11
2
3
1
12
34
56
78
910
1112
1314
1516
1718
1920
2122
2324
2526
2728
2930
3132
2
3
1
2
3
1
2
3
4
5
6
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
4
5
6
7
3
4
5
6
7
8
9
10
IG
FM
BK
BK : Black
SV
H1
SV
SV
H2
13
12
11
DU
10 0
SV
H3
V : Violet
TERMINAL A
TERMINAL C
TERMINAL B

14
CENTRAL
PROCESSING
UNIT
BURNER
FOR EXTERNAL LAMP
NO POWER SUPPLY(ONLY CONTACT)
POWER
FOR EXTERNAL LAMP
NO POWER SUPPLY(ONLY CONTACT)
PRIORITY 2
POWER SUPPLY FOR CIRCULATOR
TERMINAL B
TERMINAL C
DC15V
DC15V
RELAY 9
RELAY 4
PRIORITY 2 THERMOSTAT
PRIORITY 1
AQUASTAT
HOT NEUTRAL
PRIORITY 1
POWER SUPPLY FOR CIRCULATOR
6A FUSE
RELAY 6
RELAY 2
RELAY 1
RELAY 7
6A FUSE
RESISTANCE
RESISTANCE
GND
SWITCH
DETECT
CIRCUIT
RELAY 1
GND
RELAY
DRIVING
CIRCUIT
RELAY 6
RELAY 7
5V POWER CIRCUIT
RELAY 2
CPU
ThermostatAquastat
Priority 1
(Indirect tank)
Priority 2
(Heating)
T-T Connection
(DC15V 0.1Amp.)
TERMINAL C
For External Lamp
No Power supply(Only Contact)
Power supply for circulator
AC120Volts Max. 2.2Amp.
PowerBurner
Priority 2
(Heating)
NeutralHot
Priority 1
(Indirect tank)
Hot Neutral
TERMINAL B
TERMINAL A
Power Input
AC120Volts
GNDNeutralHot
RWWV
OOBRBRWWBK BK
BK W G
DC140V
DC140V
10A(FUSE)
ARRESTER
AC120V
AC100V
VARISTOR
RELAY 7 GAS FURNACE
PRIMARY
SECONDARY
EARTH
DC90V
HIGH LIMIT
SWITCH
A
B
A
FAN MOTOR
FAN CONTROL
OUTPUT
RELAY 3
RELAY 1
IG
SV1
SV0
RELAY 4
RELAY 5
SV2
SV3
RELAY 10
POWER
CONTROLLER
C
DC12V
PRIMARY
SECONDARY
SOLENOID
VALVE 0
SOLENOID
VALVE H1
SOLENOID
VALVE H2
SOLENOID
VALVE H3
FAN
C
B
FAN ROTATION
SPEED INPUT
FAN CURRENT
VALUE INPUT
D
WATER SUPPLY
THERMISTOR
WATER RETURN
THERMISTOR
Sub-CPU
SUB
CONTROL
UNIT
CPU
RELAY
DRIVING
CIRCUIT
RELAY 1
RELAY 3
RELAY 7
RELAY 5
CENTRAL
PROCESSING
UNIT
FAN
PULSE
CONTROL
CIRCUIT
GND
THERMAL FUSE
WATER FLOW SWITCH
15V POWER CIRCUIT
DC90V
DC15V
IGNITERRELAY 9
VARISTOR
HEAT EXCHANGER
THERMISTOR
AIR INLET
THERMISTOR
GND
5V POWER CIRCUIT
D
EARTH
DU
FR FLAME
ROD
RELAY 10
FLAME DETECTING CIRCUIT
GAS PROPORTION VALVE
POWER CONTROL CIRCUIT

15
8. Troubleshooting
103
203
903
993
1413
11 12
15
1
17
3
4
18
20
89
7
7
10
15
DescriptionDisplay
113
123
Combustion abnormality
(BTU drop)
(Warning indication)
Ignition failure
(Initial flame fault detection)
143
163
253
303
313
323
Water return thermistor
abnormality
Overheat Prevention Device
(Thermal Fuse) triggered
Water supply temperature does
not stabilize (Supply temperature
is too low)
(Heating load is too much)
High limit switch triggered
Water flow switch ON
failure
Air inlet thermistor abnormality
2
5
19
Circuit board failure
333
633
613 Fan motor abnormality
643
703
713
723
Gas valve drive circuit
abnormality
Heat exchanger thermistor
abnormality
Circuit board abnormality
Priority1 circulator abnormality
Water flow switch OFF failure
Priority2 circulator abnormality
Water flow switch OFF failure
Water supply thermistor
abnormality
Flame rod does not detect flame
(Flame fault detection)
Diagnosis Point (Trouble Point)
Check for abnormal combustion.
Check flue for blockage or obstruction.
Check the gas supply piping and pressure. Check for igniter
spark ( ). Check gas solenoid valves ( ).
Check flame rod ( ). Check ground, paying special attention to
the ground connection to the circuit board.
Check for accidental extinction of the flame. Check for abnormal
combustion. Check gas solenoid valves. Check flame rod ( ).
Check ground, especially on circuit board.
Check for melting or damage to the thermal fuse ( ).
Check for improper connection of thermal fuse.
Check the heating load. Check the supply temperature.
If the supply temperature is lower than 131°F (55°C), adjust the
flow in the heating circuit and/or check the temperature setting on
the operation panel.
Check if high limit switch is triggered ( ).
Check for improper connection of high limit switch.
Check for blocking of the water flow switch ( ).
Check for short circuit of the water flow switch.
Measure the resistance through the air inlet thermistor ( ).
Check for an open or short circuit.
Check for improper connection of air inlet thermistor.
Measure the resistance through the water return thermistor ( ).
Check for an open or short circuit.
Check for improper connection of water return thermistor.
Measure the resistance through the water supply thermistor ( ).
Check for an open or short circuit.
Check for improper connection of water supply thermistor.
Measure the resistance through the heat exchanger thermistor
( ). Check for an open or short circuit.
Check for improper connection of heat exchanger thermistor.
Check that the fan is rotating and check the pulse frequency from
the fan rotational frequency sensor ( ). Check for improper
connection of the fan. Check voltage from circuit board.
Check for damage to the gas valve drive circuit on the
circuit board.
Check that the circulator is running. Check for improper connection
of the circulator ( ). Check voltage from circuit board.
Check for improper connection of the water flow switch ( ).
Check that the circulator is running. Check for improper connection
of the circulator ( ). Check voltage from circuit board.
Check for improper connection of the water flow switch ( ).
733
903
763
760
P on
P of
Combustion abnormality
Circuit board setting abnormality
(High elevation connector,
Dip switch, etc)
Operation panel (Remote
controller) transmission
abnormality
Circuit board SC
transmission abnormality
Combustion abnormality
(Warning indication)
(The appliance is stopped)
Combustion abnormality
(The appliance is stopped)
Manual circulator
operation mode
Check for proper setting of maintenance writers on circuit board.
Check the circuit board (microcomputer) for damage.
Check the Dip switch. Check the "Control switch connector"
(ex.high elevation connector etc.).
Check connection from operation panel (remote controller) to
circuit board. Check operation panel (remote controller) and
circuit board for damage.
Check connection from circuit board SC to circuit board.
Check circuit board SC and circuit board for damage.
Check for abnormal combustion.
Check flue for blockage or obstruction.
Check for abnormal combustion.
Check flue for blockage or obstruction.
Check for abnormal combustion.
Check flue for blockage or obstruction.
P on : Water flow switch ON (Flow rate is 2.5 GPM or more)
P of : Water flow switch OFF (Flow rate is less than 2.5 GPM)
Measure the current from the flame rod when there is no flame
( ).
Check for a ground fault.
Flame rod circuit
abnormality (Detection of flame
when no flame is present)
6
Error Codes and Checkpoints
This error code is displayed when a "Control switch connector" is disconnected or connected while the
boiler has power. Disconnect power to the boiler before making this adjustment.
Control switch connectors : "High Elevation Disconnect (Fan Speed Corrector)"
"Air Flow Connector (Air Flow Switch)"
"Emergency operations only (Emergency Operations Switch)"
This error code is not mentioned in the flowchart.
Note 2)
Note 1), 2)
Note 1)
Note 1)
Note 1)
The error codes in bold cannot be reset by turning the boiler OFF on the operation panel.
Disconnect, then reconnect electrical power to the boiler to reset the system.

16
-Contact for
"BURNER" lamp
Terminal
B5BR - BR Terminal B61 Ωor less When flame is detected.
Contact resistance
-Contact for
"POWER" lamp
Terminal
B7O - O Terminal B81 Ωor less When "POWER" is ON.
Contact resistance
When valve is open
When valve is open
When valve is open
When valve is open
Remarks
32 - 212°F
0 - 100°C
32 - 212°F
0 - 100°C
2 Ωor less
Normal value
DC 1 - 4.5 V
DC 1 - 4.5 V
31
CN38
CN & Pin No.
2
2
CN63
CN63
25
CN38
CN & Pin No.
3
1
CN63
CN63
Part
1
Ref.
No.
3
4
Checkpoints
Overheat Prevention
Device (Thermal Fuse)
Water Return
Thermistor
Water Supply
Thermistor
BL - BL
Circuit board Check points
Wire color
W - W
W - W
When switch is OFF
When switch is ON
When igniter is sparking
Coil resistance
Coil resistance
Coil resistance
10 kHz - 100 kHz
DC 0.45µA or less
DC 8 - 11 V
DC 1 V or less
DC 7 - 45 V
DC 10 - 14 V
AC 108 - 132 V
-
-
-
7
2
2
7
CN75
CN27
2
Terminal
B
AC 90 - 110 V
DC 80 - 100 V
0.5 - 2 kΩ
0.5 - 2 kΩ
0.5 - 2 kΩ
DC 80 - 100 V
DC 0.3 - 15 V
DC 80 - 100 V
5
7
CN1
CN10
7
CN10
CN10 7
CN27 100 Hz - 400 Hz
2
Coil resistance
Contact resistance
When switch is OFF
10 kHz - 100 kHz
DC 1µA or more
DC 80 - 100 V
0.5 - 2 kΩ
1 Ωor less
DC 8 - 11 V
AC 108 - 132 V
-
7
-
-
CN10
6
7
4
CN1
CN75
Terminal
B
AC 90 - 110 V
AC 90 - 110 V
DC 13 - 16 V
DC 13 - 16 V
5
3
CN1
CN92
2
1
CN89 A
CN89 C
CN63 2DC 0.7 - 4.4 V
Coil resistance50 - 90 Ω
4
CN38
1
1
CN78
5
4
1
5
CN75
CN27
1
Terminal
B
Flame Rod
Priority1 Circulator
Water Flow Switch
Fan Motor
2
6
CN10
CN10
8
CN10
CN10 5
Igniter
Primary Gas
Solenoid Valve
Fan Motor CN27 3
6
7
8
2
10
11
13
12
9
Gas Solenoid Valve - 1
Gas Solenoid Valve - 2
Gas Proportioning Valve
1
3
1
CN78
CN10
3
5
3
CN1
CN75
Terminal
B
Flame Rod
Water Flow Switch
Priority2 Circulator
High Limit Switch
3
1
CN1
CN92
1
3
CN89 A
CN89 C
Power Supply
(Main Circuit Board)
Power Supply
(SC Circuit Board)
Air Inlet Thermistor CN63 5
15
16
17
18
19
-
-
-
-
20
Gas Solenoid Valve - 3
Power Supply
(Power Circuit Board)
Power Supply
(Power Circuit Board)
2
CN3814
BL -
Burnercase
Electrode
BL -
BK - W
BK - BK
BK - BK
BR - BL
R - BL
Y - BL
BK - W
W - BL
BK - BL
GY - BL
R - BL
Burnercase
BL -
BL -
Electrode
O - BL
BK - W
BK - BK
BK - W
W - W
BK - W
BL - W
BL - BL
BL - BL
5Heat Exchanger
Thermistor CN63 4CN63 2DC 1 - 4.5 V
W - W 32 - 212°F
0 - 100°C
Priority1 No calls for heat
Priority2 No calls for heat
DC 13 - 16 V
DC 13 - 16 V
80
176
70
158
2
4
Terminal
C
Terminal
C
60
140
40
104 122
50
20
12.6 8.0
30
8668
4.9 3.5 2.5 1.9 1.4
1
3
Terminal
C
Terminal
C
30
86
10
50 68
20
Priority1
T-T Connection
Priority2
T-T Connection
0
32
10
20.6
0-10
34.4
503214
-20
106.5
-4
59.6
23.7 15.5 10.3 7.0
-
-
Resistance (kΩ)
Resistance (kΩ)
Temperature (°F)
Temperature (°C)
Temperature (°F)
Temperature (°C)
V - W
R - W
DC 13 - 16 V
3
CN89
BL - BL
1
CN89- Operation Panel
(Remote Controller)
Note 3)
There is a possibility that "Water Flow Switch" has been ON though "PRIORITY1 & 2 T-T
connection" both do not call for heat (No circulation).
Note 1)
Note 1)
Note 1)
Note 2)
Note 2)
Note 2), 3)
Note 4)
Note 2)
Note 1) Water Return / Water Supply / Heat Exchanger Thermistor Temperature Characteristics
"Water flow switch ON / OFF" can be confirmed by "Maintenance Monitor".
Refer to "Maintenance Monitor List".
Note 4) Air Inlet Thermistor Temperature Characteristics

17
Error Descriptions and How to Reset
Error
Code
103
113
123
143
163
203
253
How to Fix Problem and Reset applianceContent of Error Method of detecting Error Diagnosis point (Trouble Point)No.
When igniter is sparking.
Coil resistance
Coil resistance
When valve is open.
Coil resistance
When valve is open.
Coil resistance
When valve is open.
AC 90 - 110 V
10 kHz - 100 kHz
DC 1µA or more
DC 80 - 100 V
0.5 - 2 kΩ
DC 80 - 100 V
0.5 - 2 kΩ
5
7
7
7
4
6
5
8
2
25
CN1
A blinking "103" indicates there has been a BTU drop,
but combustion will continue.
Check for abnormal combustion.
Check flue for blockage or obstruction.
Check the gas supply piping.
Ex.) "Presence of LPG gas"
"The gas was shut off with gas meter"
"Is the gas supply valve open?"
Check the gas supply pressure.
Check for igniter spark.
Check for improper connection of Igniter.
Check ground, paying special attention to
the ground connection to the circuit board.
Check the flame rod.
Check for improper connection of Flame rod.
Check ground, paying special attention to the
ground connection to the circuit board.
Check the gas solenoid valve.
Check the gas proportioning valve.
Check the manifold gas pressure.
Check flue for blockage or obstruction.
1
1
2
3
4
1
1
5
Use for 10 years or more and
combustion is abnormal.
Detection of ignition failure.
Detection of extinction of flame.
Ignition failure
(Initial flame fault detection)
Flame rod does not detect flame
(Flame fault detection)
Combustion abnormality
(BTU drop)
(Warning indication)
Please keep the gas supply pressure within the proper
pressure range.
Measurement of igniter.
Check for improper connection of igniter.
Replace igniter when the voltage is normal value but it
does not spark.
Measurement of flame rod.
Check for improper connection of flame rod.
Measurement of primary gas solenoid valve.
Check for improper connection of primary gas solenoid valve.
Measurement of gas solenoid valve-1.
Check for improper connection of gas solenoid valve-1.
Measurement of gas solenoid valve-2.
Check for improper connection of gas
solenoid valve-2.
Measurement of gas proportioning valve.
Check for improper connection of gas proportioning valve.
Measurement of overheat prevention device (thermal fuse).
Check for improper connection of overheat prevention
device (thermal fuse).
If the overheat prevention device (thermal fuse) has fused,
it has been exposed to temperature in excess 363°F.
First fix the cause of the high temperature exposure
(hole in the heat exchanger, etc) and then replace the
overheat prevention device (thermal fuse).
Add a boiler if necessary. ( Total heating load is more
than this boiler's maximum output)
* If you can drop the heat radiation, the following
methods are possible: adjust the by-pass circuit flow
rate (increase) in the heating circuit and/or check the
temperature setting on the operation panel.
Check for melting or damage to the
overheat prevention device (thermal fuse).
Check for improper connection of
overheat prevention device (thermal fuse) .
Check the gas solenoid valve.
Check the gas proportioning valve.
Check the gas supply pressure.
Check the manifold gas pressure.
Check the heating load
(calculate total heating load).
Check if high limit switch is triggered.
Check for improper connection of high
limit switch. The possibility of "Water
flow switch ON failure"
Check for blocking of the water flow switch.
Check for short circuit of the water flow switch.
The supply temperature is not
over 131°F (55°C) or more
after one hour.
It becomes an error if it repeats
three times.
Water supply temperature does
not stabilize.
(Supply temperature is too low)
(Heating load is too much)
High limit switch triggered.High limit switch triggered
Water flow switch ON failure
Overheat prevention device
(Thermal fuse) triggered.
Overheat prevention device
(Thermal fuse) triggered
Check the manifold gas pressure.
Measurement of gas solenoid valve-2. Check for improper
connection of gas solenoid valve-2.
CN & Pin No.Part
Flow chart
No.
CN10
CN10
CN10
CN10
CN38
CN38
CN10
CN10
CN38
CN10
CN10
CN38
CN10
CN10
CN10
CN38
CN38 31
CN78
Igniter
10
Flame rod
Primary gas
solenoid valve
Gas solenoid
valve-1
Gas solenoid
valve-2
Gas proportioning
valve
Overheat prevention
device (Thermal fuse)
Gas solenoid
valve-2
Gas solenoid
valve-3
Gas proportioning
valve
High limit switch
Water flow switch
CN1 BK - W
BK - BK
CN75
CN1
CN75
15
11
12
13
14
1
13
16
14
17
18
8
3
2
3
5
6
7
7
7
4
2
1
1
wire color Normal value
BK - W
CN &
Pin No. Remarks
BL - Burnercase
W - BL
BK - BL
GY - BL
R - BL
BL - BL
GY - BL
O - BL
R - BL
BL - Electrode
DC 80 - 100 V
0.5 - 2 kΩ
DC 0.3 - 15 V
DC 80 - 100 V When valve is open.
Coil resistance
50 - 90 Ω
Coil resistance
Contact resistance
When switch is OFF.
DC 0.3 - 15 V
50 - 90 Ω
0.5 - 2 kΩ
DC 80 - 100 V When valve is open.
Coil resistance0.5 - 2 kΩ
See pg. 24
See pg. 24
See pg. 26
DC 8 - 11 V
1 Ωor less
See pg. 26
2 Ωor less
Measurement of gas solenoid valve-3.
Check for improper connection of gas solenoid valve-3.
Measurement of gas proportioning valve.
Check for improper connection of gas proportioning valve.
Check the gas supply pressure.
Check the manifold gas pressure.
Measurement of high limit switch.
Check for improper connection of high limit switch.
Confirm "Water flow switch ON / OFF" by Maintenance
Monitor (No.65).
Measurement of water flow switch.
Check for improper connection of water flow switch.
Remove it if the water flow switch is blocking,

18
Error
Code
303
313
323
333
613
633
643
703
713
723
733
760
763
How to Fix Problem and Reset applianceContent of Error Method of detecting Error Diagnosis point (Trouble Point)No.
DC 0.7- 4.4 V2
5
CN63
32 - 212 °F
0 - 100 °C
32 - 212 °F
0 - 100 °C
32 - 212 °F
0 - 100 °C
2CN63
Confirm the air inlet thermistor detection temperature
by Maintenance Monitor (No.38).
Compare to temperature characteristic list on pg.16.
Check for open or short circuit or for an improper connection.
Confirm the water return thermistor detection
temperature by Maintenance Monitor (No.34).
Compare to temperature characteristic list on pg.16.
Check for open or short circuit or for an improper
connection.
Confirm the heat exchanger thermistor detection
temperature by Maintenance Monitor (No.37).
Compare to temperature characteristic list on pg.16.
Check for open or short circuit or for an improper
connection.
Confirm the water supply thermistor detection
temperature by Maintenance Monitor (No.35).
Compare to temperature characteristic list on pg. 16.
Check for open or short circuit or for an improper
connection.
Confirm the measured fan speed by Maintenance Monitor
(No.12).
If the fan motor does not rotate, but voltage is
normal, then the fan motor should be replaced.
If the voltage is abnormal, replace the circuit board.
If the fan motor is rotating and if the voltage is normal,
but there is a "613" error code, then the fan motor should
be replaced.
If the voltage is normal, but circulator is not running,
replace the circulator.
If the voltage is abnormal, replace the circuit board SC.
Measure the resistance through the air
inlet thermistor.
Check for improper connection of the
air inlet thermistor.
1
Measure the resistance through the
water supply thermistor.
Check for improper connection of the
water supply thermistor.
Measure the resistance through the
heat exchanger thermistor.
Check for improper connection of the
heat exchanger thermistor.
Measure the resistance through the water
supply thermistor.
Check for improper connection of the water
supply thermistor.
Check that the fan is rotating and check
the pulse frequency from the fan rotational
frequency sensor.
Check for improper connection of the fan.
Check voltage from circuit board.
Check the Priority1 circulator is running.
Check for improper connection of the circulator.
Check connection from circuit board SC to
Junction box.
Check whether the Priority1 circulator fuse
on the Junction Box is open.
Check for improper connection of the water
flow switch.
Check for blocking of the water flow switch.
1
1
1
1
1
3
2
1
Detection of open/short abnormality
of air inlet thermistor.
Detection of open/short abnormality
of heat exchanger thermistor.
Detection of fan speed abnormality.
Heat exchanger thermistor
abnormality
Fan motor abnormality
Air inlet thermistor abnormality
Detection of open/short abnormality
of water return thermistor.
Water return thermistor
abnormality
Detection of open/short abnormality
of water supply thermistor.
Water supply thermistor
abnormality
If the voltage is normal, but circulator is not running,
replace the circulator.
If the voltage is abnormal, replace the circuit board SC.
If Priority2 circulator fuse has blown, remove the cause
of excess current, and then replace the 6A fuse.
Check the Priority2 circulator is running.
Check for improper connection of the circulator.
Check connection from circuit board SC to
Junction box.
2
3
Check whether the Priority2 circulator fuse
on the Junction Box is open.
Circuit board abnormality.
Check connection from operation panel
(remote controller) to circuit board.
Check the operation panel (remote controller)
and circuit board for damage.
Detection of circuit board
abnormality.
Circuit board abnormality
1
Gas valve drive circuit abnormality.Detection of circuit board
abnormality.
Gas valve drive circuit abnormality
Detection of operation panel
(remote controller) transmission
abnormality.
Operation panel (remote controller)
transmission abnormality.
When the "water flow switch"
did not turn ON even if the
Priority2 circulator was turned on.
When the "water flow switch"
did not turn ON even if the
Priority1 circulator was turned on.
Priority1 circulator abnormality
Priority2 circulator abnormality
Disconnect the electrical power, then reconnect
electrical power to the boiler to reset the system.
If the circuit board abnormality is continuous, replace
the circuit board.
Disconnect the electrical power, then reconnect
electrical power to the boiler to reset the system.
If the error code "713" is continuous, replace the
circuit board.
1
1
1
Detection of circuit board SC
transmission abnormality.
Circuit board SC transmission
abnormality
1
2
Measure the current from the flame
when there is no flame.
Check for "Control switch connector"
is disconnected or connected while
the boiler has power.
Check for proper setting (Dip switch).
Detection of flame when no
flame is present.
Detection of circuit board
setting abnormality.
Circuit board setting abnormality
(High elevation connector,
Dip switch, etc.)
Flame rod circuit abnormality
(Detection of flame when no
flame is present)
If the "723" error code is displayed, check the signal
from the flame rod (also make sure that there is not a
problem with the grounding of the appliance).
If the signal is normal, replace the circuit board.
If it is abnormal, replace the flame rod.
Check the Dip switch setting.
If a setting is incorrect, correct the Dip switch setting.
This error code is displayed when the "Control switch
connector" is disconnected or connected while the
boiler has power. Disconnect power to the boiler
before making this adjustment.
Control switch connectors:
*High Elevation Disconnect
(Fan Speed Corrector)
*Air Flow Connector (Air Flow Switch)
*Emergency operations only
(Emergency Operations Switch)
CN & Pin No.Part
Flow chart
No.
CN63
CN63
CN75
CN78
CN89A
CN89
CN89A
CN89
1
1
2
3
BL - BL
BL - BL
7
Air inlet thermistor
Water return
thermistor
20
Flame rod
5
8
9
2
7
7
19
6
1
1
5
33
wire color Normal value
W - W
DC 1- 4.5 V
DC 1- 4.5 V
2CN63
CN63
Water supply
thermistor
Fan motor
Priority1
circulator fuse
Priority1
circulator fuse
Water flow switch
Priority2 circulator fuse
Priority2 circulator
Water flow switch
41W- W
DC 1- 4.5 V2CN63
CN63
CN27
Te r minal
B
Te r minal
B
CN75
CN75 CN75
Te r minal
B
Te r minal
B
Heat exchanger
thermistor 4
4
1
3
W - W
BR - BL
R - BL
BK - W
BK - BK
BK - W
BK - BK
CN27
Y - BL
Junction box
Junction box
W - W
CN &
Pin No. Remarks
BL - Burnercase
BL - Burnercase
If Priority1 circulator fuse has blown, remove the cause
of excess current, and then replace the 6A fuse.
Confirm "Water flow switch ON / OFF" by Maintenance
Monitor (No.65).
If the circulator is running, but water flow switch is OFF,
check the flowrate and adjust if necessary.
Remove it if the water flow switch is blocked.
Check for improper connection of the water
flow switch.
Check for blocking of the water flow switch.
Confirm "Water flow switch ON / OFF" by Maintenance
Monitor (No.65).
If the circulator is running, but water flow switch is OFF,
check the flow rate and adjust if necessary.
Remove it if the water flow switch is blocked.
10 kHz - 100 kHz
DC 0.45µA or less
If there is a voltage abnormality, replace the circuit board.
If a voltage is normal, replace the operation panel
(remote controller).
Check connection from circuit board SC to
circuit board.
Check the circuit board SC and circuit board
for damage.
If there is a voltage abnormality, replace the
circuit board.
If a voltage is normal, replace the circuit board SC.
2
2
2
1
5
3
2
7
4
DC 7 - 45 V
DC 10 - 14 V
AC 108 - 132 V
Closed circuit
Closed circuit
DC 8 - 11 V When switch is OFF.
When Priority1 calls
for heat.
AC 108 - 132 V When Priority2 calls
for heat.
When switch is ON.DC 1 V or less
100 Hz - 400 Hz
DC 8 - 11 V When switch is OFF.
When switch is ON.DC 1 V or less
DC 13 - 16 V
DC 13 - 16 V
CN89C
CN89
CN89C
CN89
3
1
1
3
BL - BL
BL - BL
DC 13 - 16 V
DC 13 - 16 V

19
Error
Code
903
993
No
Error
Code
How to Fix Problem and Reset applianceContent of Error Method of detecting Error Diagnosis point (Trouble Point)No.
If abnormal combustion is detected, the error code will
flash and combustion stops.
This error code can be reset by turning the boiler OFF
on the operation panel.
Remove the cause of the abnormal combustion.
Check maintenance monitor No.66. If the fan has
increased its speed by 108 - 109 %, the error code will
flash but combustion continues. If the fan has
increased its speed by 110 %, the error code will flash
and combustion stops.
If this error code is displayed and the boiler has been
in use for 10 years, the boiler has reached the end of
its life cycle and should be replaced.
Check for improper connection of "Junction Box"
or "Transformer".
Remove the cause of excess current, and then
replace the 10A fuse.
Check for abnormal combustion.
Check flue for blockage or obstruction.
1
Check for abnormal combustion.
Check flue for blockage or obstruction.
The electrical power does not connect.
Check the electrical power input.
The electrical power is not supplied to
the circuit board.
Check the electrical power input.
A fuse is blown.
Check whether the 10A fuse on the
power circuit board is open.
If there is a voltage abnormality, replace the
circuit board.
If a voltage is normal, replace the operation
panel (remote controller).
Check connection from operation panel
(remote controller) to circuit board.
Check the operation panel (remote controller)
and circuit board for damage.
The circulator automatically operates for
combustion to prevent freezing.
Has Priority1 been running for an
extensive period?
The room does not get warm.
The heating does not operate.
1
1
2
3
4
1
1
1
Detection of combustion
abnormality.
The operation panel
(remote controller) is not turned
ON (No indication) though
"Power button" was pushed.
Burner ON Indcator is lit even when
the Power button is set to OFF.
Burner ON Indcator is lit even when
the Priority1 or 2 is not being used.
In this case, the set temperature of the aquastat
controlling the indirect tank may be higher than the
set temperature of this appliance.
Change to a correct temperature setting.
Combustion abnormality
Combustion abnormality
(Warning indication)
(The appliance is stopped)
Detection of combustion
abnormality.
Combustion abnormality
(The appliance is stopped)
Refer to "User's information manual" P.11.
It is not abnormal.
It is not abnormal.
1
2
3
These noises indicate the proper operation of
devices which are designed to let the
appliance reignite more quickly, and ensure
temperature of the boiler water is stable.
It is not abnormal.
It is not abnormal.
The sound is from the circulator operating to
prevent freezing.
This appliance automatically operates
the circulator for several seconds when
the appliance has not been used for
approximately 15 days to prevent the
circulator from malfunctioning due to
build-up of deposits.
Priority2 (Heating use) will stop even
during operation when Priority1
(Indirekt tank use) operation starts.
The heating turns off by itself
during heating and there is no
warm air.
Operation sounds are heard from
the boiler even though it is not
being used.
1
Check for improper connection of
Priority1 T-T connection ("From circuit
board SC to terminal C" or
"From terminal C to Aquastat").
The appliance does not operate
even if there is a call for heat.
If there is a voltage abnormality, replace the
circuit board SC.
If a voltage is normal, replace the Aquastat.
2
Check for improper connection of
Priority2 T-T connection ("From circuit
board SC to terminal C" or "From
terminal C to Room thermostat").
If there is a voltage abnormality, replace the
circuit board SC.
If a voltage is normal, replace the Room
thermostat.
CN & Pin No.Part
Flow chart
No.
2
1
wire color Normal value
3
CN 92
CN89A
CN89
CN89A
CN89
1
1
1
BL - W
AC 108 - 132 V
AC 90 - 110 V
Closed circuit
2
Te r minal
A
CN 92
Te r minal
A
1 BK - W
BL - BL
BL - BL
CN &
Pin No. Remarks
V - W
Te r minal
C
Te r minal
C
It is not abnormal.
DC 13 - 16 V Priority1 does not call
for heat
2
3DC 13 - 16 V
DC 13 - 16 V
Priority1
T-T connection
4
3R - W
Te r minal
C
Te r minal
C
DC 13 - 16 V Priority2 does not call
for heat
Priority2
T-T connection

20
Displaying Maintenance Monitors on the Operation Panel (Remote Controller)
< Display Procedure >
1. Press and hold both the up [] and down [] Temperature adjustment buttons simultaneously for more than 2 seconds.
This can be done regardless of whether the power has been turned on or the boiler is operating.
Note 1) Please turn on the "Power button" once after connecting the electrical power.
Note 2) Maintenance monitors cannot be displayed while in "Manual circulator operation mode".
< Indications >
1. The maintenance monitor data No. will appear on the display for 2 seconds, and then the data willappear.
2. In order to switch to other maintenance monitor data, press either the up [] or down [] button once.
The data No. will then reappear, then different data No. can be selected using the up [] or down [] buttons.
When the maintenance monitor data No. is changed, the data No. will be displayed for 2 seconds, after which the data
will appear.
3. With the operation panel (remote controller) in maintenance monitor mode, "Supply temperature" cannot be adjusted.
< Returning to Normal mode >
1. For releasing the indication, press and hold both the up [] and down [] Temperature adjustment buttons simultaneously
for more than 2 seconds, or leave it alone for more than 10 minutes.
< Clearing Error Codes from Memory >
When the Power button is OFF, press and hold the down [] button for more than 5 seconds.
When a "beep" sound is heard, the error codes have been cleared.
Temperature adjustment buttons
Priority2 indicator (green)
Burner ON indicator (red)
Priority1 indicator (orange)
User setting button
Priority1 button
Priority2 button
Display
Operation panel (Remote controller)
Power indicator (green)
Power button