Bosch Singular 4000 User manual

Service Manual
Gas Condensing Combi Boilers
Singular
Singular 4000 | Singular 5200
BTC 439002301 A / 12.2021
WARNING:
If the information in these instructions are not followed exactly, a fi re or explo-
sion may result causing property damage, personal injury or death.
WARNING:
Do not store or use gasoline or other fl ammable vapors and liquids in the vicinity
of this or any other appliance.
WHAT TO DO IF YOU SMELL GAS
—Do not try to light any appliance.
—Do not touch any electrical switch; do not use any phone in your building.
—Immediately call your gas supplier from a neighbor’s phone. Follow the gas
supplier’s instructions.
—If you cannot reach your gas supplier, call the fire department.
WARNING:
Improper installation, adjustment, alteration, service or maintenance can cause
property damage, personal injury (exposure to hazardous materials)* or loss of
life. Refer to the user's information manual provided with this boiler. Installation
and service must be performed by a qualifi ed installer, service agency or the gas
supplier who must read and follow the supplied instructions before installing,
servicing, or removing this boiler. This boiler contains materials that have been
identifi ed as carcinogenic, or possibly carcinogenic, to humans.
This boiler must be installed in accordance with local, state, and federal codes.
In the absence of such requirements, then to the latest edition of the National
Fuel Gas Code, ANSI Z223.1./NFPA 54. In Canada, installation must be in
accordance with the requirements of CAN/CSA B149.1, Natural Gas and
Propane Installation Code.

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Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)

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Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)
Table of Contents
1 Key to Symbols and Safety Instructions 4
1.1 Key to Symbols 4
1.2 Safety 4
2 Key Components 6
3 Technical Data 8
4 Dimensions 9
5 Setting the DIP Switches 10
6 Wiring Diagram 11
7 Key Components Description 12
7.1 Pump 12
7.2 Turn Down Ratio (TDR) Solenoid valve 12
7.3 Orifi ce 13
7.4 Fan 13
7.6 High Limit Cutout HEX T2 (302°F) 14
7.7 High Limit Cutout Supply T3 (203°F) 14
7.8 Primary Heat Exchanger 14
7.9 Secondary Heat Exchanger 15
7.10 Sensor 15
7.11 Electrode 16
7.12 Flame Rod 16
7.13 Ignition Transformer & Wire 16
7.14 Burner 17
7.15 Gas Valve 17
7.16 Touch Pad 17
7.17 Control Board 18
7.18 Condensate Trap Assembly 18
7.19 Air Pressure Switch 18
8 Troubleshooting 19
8.1 A2 Error (Abnormal Operation: Fan) 19
8.2 A3 Error (Abnormal Operation: Pump) 21
8.3 A4 Error (Overheating of Heat Exchanger) 23
8.4 A5 Error (Low Water Pressure) 25
8.5 A6 Error (Ignition Error) 27
8.6 A7 Error (Abnormal Operation: Gas Valve Relay) 29
8.7 A8 Error (Abnormal Operation: Gas Valve) 29
8.8 A9 Error (Exhaust Temperature Sensor Error) 31
8.9 AA Error (Overheating) 33
8.10
AB Error (Abnormal Operation: Heat Exchanger Temperature Sensor 34
8.11 AC Error (Abnormal Operation: DHW Sensor) 36
8.12 AD Error (Clog of Condensate Trap) 38
8.13 AE Error (Blockage of Flue Pipe) 40
8.14 EO Error (Abnormal Operation: Outdoor Temperature Sensor) 42
8.15 E1 Error (Abnormal Operation: Exhaust Temperature Sensor) 44
8.16 E2 Error (Exhaust Temperature Overheating) 46
8.17 E3 Error (Abnormal Operation: Return Sensor) 48
8.18 E4 Error (Abnormal Operation: Pressure Sensor) 50
8.19 E7 Error (Abnormal Operation: Gas Valve Relay) 52
8.20 EB Error (Hot Water Overheating) 52
9 Components Replacement Instructions 54
9.1 Preparation Step 54
9.2 Control Board 55
9.3 Sensor, Heating/Return 55
9.4 Sensor, DHW 55
9.5 Exhaust Temperature Sensor_T4 (Blue) 55
9.6 Gas Orifi ce 56
9.7 Air Pressure Switch 56
9.8 Gas Valve 57
9.9 High Limit Cutout HEX T2 (302°F) 57
9.10 High Limit Cutout Supply T3 (203°F) 57
9.11 Ignition Transformer 57
9.12 Electrode Assembly 58
9.13 Flame Rod 58
9.14 Touch pad 59
9.15 Condensation Trap 59
9.16 Turbo Fan 60
9.17 Solenoid Valve 61
9.18 Heat Exchanger 62
10 Flushing the Heat Exchanger 65

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Singular Combi Boiler - BTC 439002301 A (12.2021)
1 Key to Symbols and Safety Instructions
1.1 Key to Symbols
Warnings
Warnings in this document are identifi ed by a
warning triangle printed against a grey background.
Keywords at the start of a warning indicate the type and seriousness
of the ensuing risk if measures to prevent the risk are not taken.
The following keywords are defi ned and can be used in this document:
DANGER indicates a hazardous situation which, if not avoided, will result
in death or serious injury.
WARNING indicates a hazardous situation which, if not avoided, could
result in death or serious injury.
CAUTION indicates a hazardous situation which, if not avoided, could
result in minor to moderate injury.
NOTICE is used to address practices not related to personal injury.
Important information
This symbol indicates important information where
there is no risk to people or property.
1.2 Safety
Please read before proceeding
WARNING: FIRE, EXPLOSION
Vapors from flammable liquids can explode and/or catch fire
causing death or severe burns.
Keep flammable products far away from the boiler and store
them in approved containers. Keep the containers tightly
closed and out of the reach of children.
The boiler has a main burner flame that can come on at any
time and will ignite flammable vapors.
Vapors cannot be seen and are heavier than air. They can
travel long distances along the ground and can be carried
from other rooms to the boiler’s main burner flame by air
current.
WARNING: SCALD HAZARD
Water temperature over 125°F can cause severe burns or
death from scalding.
If it is necessary to set the water temperature above 125°F
(52°C), consider installing a thermostatically-controlled
mixing valve. Contact a licensed plumber or your local
plumbing authority for more information.
Children, the disabled and the elderly are at highest risk of
being scalded.
Test water before bathing or showering.
Temperature Time to Produce Serious Burn
120 °F (48 °C) More than 5 minutes
125 °F (51 °C) 1.5 to 2 minutes
130 °F (54 °C) Approx. 30 seconds
135 °F (57 °C) Approx. 10 seconds
140 °F (60 °C) Less than 5 seconds
145 °F (62 °C) Less than 3 seconds
150 °F (65 °C) Approx. 1.5 seconds
155 °F (68 °C) Approx. 1 second
Table 1
WARNING: RISK OF PERSONAL INJURY OR DEATH FROM EXPLOSION!
Work on gas components may only be carried out by a
trained and certified installer or service company.
Appliance installation, the connection of gas and vent
piping, initial commissioning, electrical connections, and
service and maintenance must only be carried out by a
trained and certified installer or service company.

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WARNING: FIRE, EXPLOSION
Do not store combustibles, such as papers or laundry, near
the boiler or venting system.
 Do not store or use gasoline or other flammable liquids near
this boiler.
Do not store or use compressed gases, such as hair sprays
or spray paints, near the boiler or venting system, including
the vent termination.
WARNING: HAZARDOUS VOLTAGE
Do not remove the front cover unless the power to the boiler
is turned off or disconnected.
Do not touch the internal components of the boiler or the
power cord with wet hands.
WARNING: FIRE, CARBON MONOXIDE
Do not operate the boiler with the front cover opened.
Do not operate the boiler without proper venting.
Do not place anything in or around the vent terminals that
could obstruct the air fl ow in or out of the boiler.
WARNING: FIRE, EXPLOSION
Have your installer or plumber show you the location of the
gas shut off valve and demonstrate how to close the valve. If
the boiler is damaged as a result of overheating, fire, flood,
or any other reason, close the manual shut off valve and do
not operate the boiler again until it has been inspected by a
qualified technician.
WARNING: FIRE, EXPLOSION
Should overheating occur or if the gas supply fails to shut
off, turn off the manual gas shut off valve.
WARNING: PERSONAL INJURY, PROPERTY DAMAGE
Do not allow children to operate or have access to the boiler.
WARNING: IMPROPER OR DANGEROUS OPERATION
Immediately call a qualified service technician to inspect the
appliance and replace any part of the control system and/or
any gas control which has been immersed in water.
WARNING:
This product can expose you to chemicals including Lead
and Lead components, which are known to the State
of California to cause cancer and birth defects or other
reproductive harm. For more information go to www.
P65Warnings.ca.gov.
WARNING: FIRE, CARBON MONOXIDE
After replacement of a gas related component, where a
gasket of seal has been disturbed or replaced, check for gas
tightness using a gas detector / analyzer.
On re-assembly check all affected seals for cracks hardness
and deterioration. If damaged or in any doubt the seal must
be replaced.
CAUTION: INTENDED USE
Do not use the boiler for anything other than its intended
purpose, as described in this manual.
CAUTION: IMPROPER OR DANGEROUS OPERATION
Do not use unapproved replacement or accessory parts.
When servicing the controls, label all wires prior to
disconnecting them to prevent wiring errors.
Do not attempt to repair or replace any part of the boiler,
unless it is specifically recommended in this manual. For all
other service, contact an authorized technician or licensed
professional. Improper adjustments, alterations, service, or
maintenance may lead to property damage, personal injury,
or death and will void your warranty.
NOTICE: BOILER DAMAGE
Do not turn on the boiler unless the water and gas supplies
are fully opened. Failure to do so may damage the boiler.

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Singular Combi Boiler - BTC 439002301 A (12.2021)
2 Key Components
Figure 1
Air intake connector
Gas connector/Orice
Gas valve
3-way valve
Pressure sensor
Space heating supply
Gas inlet
Hot water outlet
Burner hood
Heat Exchanger Cover
Pump
Air vent
Condensate drain
Space heating return
Cold water inlet
Exhaust temperature
sensor
Flue connector
Heating temperature
sensor (T2)
Return temperature
sensor
DHW temperature
sensor

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Singular Combi Boiler - BTC 439002301 A (12.2021)
Figure 2
Ignition transformer
Control Board
Touch Pad
Secondary heat
exchanger
Primary heat
exchanger
Flow sensor
Air Pressure Switch
TDR damper
Water Pressure Sensor
Turbo fan assembly
High Limit Cutout
Supply T3 (203°F)
High Limit Cutout
HEX T2 (302°F)
Condensate Trap
Flame rod
Electrode assembly

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Singular Combi Boiler - BTC 439002301 A (12.2021)
3 Technical Data
Singular 4000 Singular 5200
Heat Capacity (Input) Space Heating 19,900–80,000 BTU/H 19,900–140,000 BTU/H
Domestic Hot Water 19,900–155,000 BTU/H 19,900–199,000 BTU/H
Flow Rate (DHW) 45°F (25°C) Temp Rise 6.0GPM (23LPM) 7.7GPM (29LPM)
67°F (37°C) Temp Rise 4.0GPM (15LPM) 5.2GPM (20LPM)
AFUE Natural Gas (propane) 95.0% (95.0%) 95.0% (95.0%)
Dimensions (W x D x H) 18.1“ x 27.6” x 11.6“ (460 mm x 700 mm x 295 mm)
Installation Type Indoor wall-hung
Venting Type Forced draft direct vent
Ignition Electronic ignition
Water Pressure(Hydronic/DHW) 12~30psi /15~150 psi
Supply Pressure Natural Gas 3.5" – 10.5" WC
Propane 8" – 13" WC
Temperature Range Space Heating 82°F – 180°F(27°C – 82°C)
DHW 86°F – 140°F(31°C – 60°C)
Minimum Flow Rate (DHW) 0.5GPM(2.0LPM)
Power Supply Main Supply 120V AC, 60 Hz / uses less than 5 AMP
Connection Sizes
Space heating Supply/Return 1" NPT
Cold water Inlet 3/4" NPT
Hot Water Outlet 3/4" NPT
Gas Inlet 3/4" NPT
Materials Primary Heat Exchanger Stainless steel
Secondary Heat Exchanger Stainless steel
Venting
Exhaust/Intake "2"" or 3"" PVC, CPVC, Polypropylene
2"" or 3"" Special gas vent type BH (Class II, A/B/C)"
Length 2" 60ft(18.3m)
3" 150ft(45.7m)
Vent Clearances 0" to combustibles
Safety Devices Flame rod, APS, Over heat preventer, Low water cut off switch,
Exhaust temperature high limit sensor, Power surge fuse
Table 2

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Singular Combi Boiler - BTC 439002301 A (12.2021)
4 Dimensions
Figure 3
2.80"
(71.1 mm) 0.36" (9.2 mm)
18.11" (460 mm)
5.57"
(141.5 mm)
5.26"
(133.5 mm)
11.61" (295 mm)
G
H
4.0"
(101.6 mm)
3.6"
(91.4 mm)
2.7"
(68.6 mm)
1.6" (40.6 mm)6.1"
(154.9 mm)
2.8"
(71.1 mm)
3.4"
(86.4 mm)
4.7" (119.4 mm)
2.2"
(55.9 mm)
8.0" (203.2 mm)
A B C D E F 1.8"
(45.7 mm)
27.56" (700 mm)
31.87" (809.5 mm)
Position Description Diameter
A Space heating Return 1" NPT
B Cold water inlet 3/4" NPT
C Condensate Outlet 1/2" NPT
D Hot water Outlet 3/4" NPT
E Space heating Supply 1" NPT
F Gas Inlet 3/4" NPT
G Exhaust Vent 2"
H Air inlet 2"
Table 3

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Singular Combi Boiler - BTC 439002301 A (12.2021)
5 Setting the DIP Switches
The boiler has a DIP switch on the main circuit board (PCB)
Set the DIP switch appropriately, depending on the installation environment.
Switch Function
Temperature limit switch for exhaust gas ON: No temperature limit for exhaust gas
OFF: Temperature limit for exhaust gas
EEP ROM data change switch ON: Enable EEP ROM data change
OFF: Disable EEP ROM data change
Long fl ue Length 1 DIP S/W #3 DIP S/W #4
FLUE LENGTH
2” PVC 3” PVC
OFF OFF Up to 15' Up to 150'
Long fl ue Length 2
OFF ON Up to 30'
N/AON OFF Up to 45'
ON ON Up to 60'
N/A N/A
Minimum heat capacity operation ON : Minimum operation
OFF : Normal operation
Maximum heat capacity operation ON : Maximum operation
OFF : Normal Operation
N/A N/A
Table 4 Dip Switches

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Singular Combi Boiler - BTC 439002301 A (12.2021)
6 Wiring Diagram
Figure 4
Over Heat Thermostat
DC FAN
Flame Rod
White
Black
120VAC,5A
Power
White
Green
Black
( AC 120V )
Ignitor (AC 120V)
Air Pressure Switch
Ground
CIR
MAX
MIN
HB
Yellow
White
Black
Red
CAS
Ex2
Ex1
PRG
RST
Black
Red
White
Black
Brown Brown
Blue
Black
Red
(Solenoid Valve)
T.D.R Damper
Gas Valve
Red
Red
Pressure Sensor Red
Flow Detect Switch
Black
Purple
White
White
High Limit Cutout
Yellow
Yellow
Touch Pad
3-way Valve
PUMP
White
White
Green
Green
Blue
Blue
SRW Red
SRW Red
Condensate trap
Blue
Blue
Green
Red
Gray
Gray
Black
Black
Black
GND
OPTION
RCOP
Brown Brown
Outdoor
Thermistor
OPTION
Domestic
Hot Water
Thermistor
Space Heating
Supply
Thermistor
Space Heating
Return
Thermistor
Zone Control Wire (TT)

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Singular Combi Boiler - BTC 439002301 A (12.2021)
7 Key Components Description
7.1 Pump
Part No. 7738007283
Function
Carries out combustion by circulating the water in the pipe.
Circulates the water when the water temperature is 59°F (15°C) or
below to prevent the boiler from freezing and bursting.
Failure Event Unable to detect or measure water pressure change when the pump
operates.
Effects The device may freeze.
The boiler does not operate.
Error Code —
Diagnostic Visual inspection : Check the circulation pump connection wire
Voltage check : Check range of voltage shown below
Color/Number of Wires
BLACK - WHITE
ON: AC 120 V ±
OFF: 0 V
Table 5
7.2 Turn Down Ratio (TDR) Solenoid valve
Part No. 7738007264
Function To control the amount of mixed gas supplied with TDR of 10:1
It uses solenoid valve to control the amount of mixed gas
Failure Event Solenoid valve not closing
Solenoid valve not opening
Effects Frequent On/Off due to excessive heat.
Fail to reach the set temperature due to lack of heat
Error Code —
Diagnostic Visual inspection : Check the Solenoid valve connection wire
Voltage check : Check range of voltage shown below
Color/Number of Wires RED - RED
DC : 120 V ±
Table 6

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7.3 Orifi ce
Part No. 7738007257 (NG)
7738007258 (LP)
Function Control the gas pressure and provide the proper quantity of the gas.
Failure Event Making combustion noise.
Imperfect and lifting flame occurs.
Effects Making a noise.
Excess carbon monoxide emissions.
Error Code N/A
Diagnostic Visual inspection: Check the gas type.
Color/Number of Wires N/A
Table 7
7.4 Fan
Part No. 7738007262
Function
Providing combustion air and gas.
To make the ideal combustion, exhaust the flue gas before and after
the combustion.
Failure Event
Fan speed failure: in case that the fan RPM is less than or equal to
600 RPM.
The fan assembly screw loosens, or the fan is damaged.
Connection of the wire connector in fault.
Effects
Unstable combustion condition.
Unit vibrating and making a noise.
The water heater is not operated.
Error Code A2
Diagnostic Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Color/Number of Wires
Black-Red: DC 5 – 45 V
Black-Yellow: DC 12 V
Black-White: 600 – 8100 RPM
Table 8

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Singular Combi Boiler - BTC 439002301 A (12.2021)
7.6 High Limit Cutout HEX T2 (302°F)
Part No. 7738007253
Function Due to the excessively high temperatureof the Heat Exchanger (HEX), it will
trip and stop combusting.
Failure Event Unable to detect the excessively high temperature if the cutout fails.
Effects Unable to stop combusting if the heat exchanger temperature exceeds
302°F (150°C)
Error Code A4
Diagnostic Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Color/Number of Wires Red-Red: DC 5 V
Table 9
7.7 High Limit Cutout Supply T3 (203°F)
Part No. 7738007275
Function Due to the excessively high supply water temperature, it will trip and stop
combusting.
Failure Event Unable to detect the excessively high supply water temperature if the
cutout fails.
Effects Unable to stop combusting if the water temperature from the heat
exchanger exceeds 203°F (95°C)
Error Code A4
Diagnostic Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Color/Number of Wires Red-Red: DC 5 V
Table 10
7.8 Primary Heat Exchanger
Part No. 7738007256*
Function
Main part for heat transfer from the burner
It has multiple paths of water tubes on the heat exchanger surface as
well as inside the combustion chamber.
Failure Event
Water and/or exhaust gas leakage through a crack
Improper heat transfer can cause the water in the heat exchanger to
boil due to possible scale formation
Effects Leakage of exhaust gas
Excessive heating of water that produces boiling noises.
Error Code AA, A4
Diagnostic
Visual inspection : Check if there is a crack on the surface of heat
exchanger.
Sound inspection : Check if boiling occurs inside the unit
Color/Number of Wires N/A
Table 11
* part number is for fully assembled heat exchanger unit.

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Singular Combi Boiler - BTC 439002301 A (12.2021)
7.9 Secondary Heat Exchanger
Part No. 7738007256*
Function
Main part for heat transfer from the burner
It has multiple paths of water tubes on the heat exchanger surface as
well as inside the combustion chamber.
Failure Event
Water and/or exhaust gas leakage through a crack
Improper heat transfer can cause the water in the heat exchanger to
boil due to possible scale formation
Effects Leakage of exhaust gas
Excessive heating of water that produces boiling noises.
Error Code AA, A4
Diagnostic
Visual inspection : Check if there is a crack on the surface of heat
exchanger.
Sound inspection : Check if boiling occurs inside the unit
Color/Number of Wires N/A
Table 12
* part number is for fully assembled heat exchanger unit.
7.10 Sensor
Part No.
7738007297 (Sensor, Supply/Return)
Sensor, Heating/Return
Sensor, DHW
Exhaust Temperature Sensor (Blue)
7738007295 (Sensor, DHW)
7738007268 (Exhaust Temperature Sensor)
Function Measure the temperature of the hot water, cold water, exhaust gas in the
boiler.
Failure Event Unable to properly measure the temperature in the boiler.
Effects
Unable to shut combustion off when the water temperature from the
heat exchanger exceeds 203°F (95°C).
Unable to reach the hot water temperature set by user.
Unable to shut down the water heater when the flue gas temperature
from the exhaust duct exceeds 203°F (95°C).
Error Code AA, AB, AC, E1, E2, E3, EB
Diagnostic
Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Resistance check of the sensor.
Color/Number of Wires Blue-Blue: DC 0 – 5 V
Table 13

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Singular Combi Boiler - BTC 439002301 A (12.2021)
7.11 Electrode
Part No. 7738007260
Function To ignite the gas, discharge the spark to the main burner repeatedly until
igniting the gas.
Failure Event Unable to ignite during the ignition process.
Effects
The unit cannot ignite during the ignition process and “A6” error code
will be shown on the display panel.
No effects on the unit, however, the durability of the spark plug are
down.
Error Code A6
Diagnostic Visual inspection: Connection or breakage of wires.
Color/Number of Wires N/A
Ignitor Gap Distance 4.0 – 4.8 mm (0.16“ – 0.19”)
Table 14
7.12 Flame Rod
Part No. 7738007259
Function Detect the normal fl ame during the combustion.
Failure Event Fail to detect a flame in spite of the combustion process.
Improper gap
Effects The boiler is not operated.
Error Code A6, A8
Diagnostic
Visual inspection: Connection or breakage of wires, check the flame
rod gap.
Check range of voltage shown below.
Color/Number of Wires White-Ground : AC 24 V
Table 15
7.13 Ignition Transformer & Wire
Part No. 7738007252
Function To ignite the gas, discharge the high voltage spark to the main burner.
Failure Event Unable to ignite during the ignition process.
Effects The unit cannot ignite during the ignition process and “A6” error code will
be shown on the display panel.
Error Code A6
Diagnostic Visual inspection: Connection or breakage of wires.
Check range of voltage shown below.
Color/Number of Wires Brown-Brown: AC 120 V
Input Voltage 120 V, 60 Hz
Output Voltage 18 kV
Table 16

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Singular Combi Boiler - BTC 439002301 A (12.2021)
7.14 Burner
Part No. 7738007256*
Function Combustion with a mixture of gas and air.
Failure Event
Unable to initialize/sustain combustion.
Foreign substance or soot deposit on the burner surface.
Gas leakage from the burners.
Effects
Unexpected combustion.
Unstable flame condition and flame lifting.
Ignition failure.
Excess carbon monoxide emissions.
Error Code A6
Diagnostic Visual inspection: Excess foreign substance on the burner surface and
unstable fl ame condition during combustion.
Color/Number of Wires N/A
Table 17
* included in heat exchanger assembly
7.15 Gas Valve
Part No. 7738007270
Function
Provide the gas for combustion.
For some reason, it shuts off the gas valve automatically and prevents
an unsafe condition due to combustion .
Failure Event Gas leak from the valve.
Unable to open/close.
Effects Gas leak from the unit.
The unit does not operate.
Error Code A6, A8
Diagnostic Visual inspection: Disconnection or breakage of wires.
Check range of voltage shown below.
Color/Number of Wires White-White: DC 120 V
Table 18
7.16 Touch Pad
Part No. 7738007238
Function Turn the boiler on or off , adjust the water temperature, and change the
modes.
Failure Event Malfunction of Touch Pad
Effects No operation of unit.
Error Code EE
Diagnostic Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Color/Number of Wires Yellow-Yellow: DC 24 V
Table 19

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7.17 Control Board
Part No.
7738007249 (Singular 5200)
7738007248 (Singular 4000)
Function To control each component and performance of unit.
Failure Event Malfunction of control board.
Unit does not operate.
Effects
A component does not operate within the unit.
In case of the control board failure, the water heater does not
operate.
Error Code —
Diagnostic Visual inspection: Connection or breakage of water or burn marks on the
control board.
Color/Number of Wires N/A
Table 20
7.18 Condensate Trap Assembly
Part No. 7738007273
Function Drain condensation, which is created while combusting.
Failure Event Fail to drain condensation caused by clogged trap.
Condensation leakage into the unit.
Effects Stop combustion.
Condensation leakage.
Error Code AD
Diagnostic
Visual inspection: Connection or breakage of wires, check for
physical damage to the trap body.
Voltage Check: Check range of voltage shown below.
Color/Number of Wires Green-Red: AC 24 V
Table 21
7.19 Air Pressure Switch
Part No.
7738007247 (Singular 5200)
7738007246 (Singular 4000)
Function Prevents operation of the unit due to unsafe condition. Back pressure or
blockage has occurred in the exhaust vent.
Failure Event No operation of the unit.
Effects Stop combustion.
No operation of the unit.
Error Code AE
Diagnostic Visual inspection: Connection or breakage of wires.
Voltage check: Check range of voltage shown below.
Color/Number of Wires Green-Green: DC 5 V
Table 22

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Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)
8 Troubleshooting
8.1 A2 Error (Abnormal Operation: Fan)
Error Description
Turbo fan RPM error Error occurs when the RPM is not measured due to no turbo fan operation or a defect of the hall sensor
Checkpoint
Check the connection of the wire
Check the fan wire for disconnection
Check the PCB output voltage
—Red-Black: 0 – 45 V
—Yellow-Black: 0 – 13 V
Table 23
Figure 5
Check the assembly
condition of the control board
and the fan connector.
Reassemble the control board
and the fan connector.
Replace the control board
Replace the fan
Replace the fan
Replace the control board
Power ON / faucet ON
(1 GPM)
Check
the fan input
voltage
Fan operation
Check
the FAN Hz
Yes
Yes
Yes
No
No
No
Red-Black: 5 45 V
Black-Yellow: 10 13 V

20 |
Service Manual
Singular Combi Boiler - BTC 439002301 A (12.2021)
A2 Error - Wire Check
1. Check the connection of the Fan Connector Wire (Red-Black).
2. Check the connection of the Hall IC Connector Wire (Yellow-White).
Figure 6
Fan
Connector
Wire Hall IC
Connector
Wire
3. Check the connection of the control board Connector Wire (Red-Black).
Figure 7
Control
Board
Connector
A2 Error - Control board Input Voltage Check
1. Measure the control board input voltage (measure while using the hot water)
Multi tester range: “DC V”
Measurement Method Measured value
Measure the applied voltage Red - Black: DC 5 – 45 V
Yellow – Black: DC 10 – 13 V
Measure FAN Hz White – Yellow: 0 – 270 Hz
Table 24
Figure 8
V
Applied Voltage Measurement Method
Figure 9
Hz
FAN Hz Measurement Method
2. If the voltage is measured normally but the fan does not operate, replace the
fan.
3. If the fan operates but Hz cannot be measured, replace the fan.
4. If the voltage cannot be measured, replace the control board.