State AGT-705-NE Service Manual
On-Demand Gas Tankless
Water Heater Service Manual
Service information for single and multiple unit installations
for residential, commercial, recirculation and storage tank systems.
Series 100/101 & Series 200/201
ATI-305-N GTS-305-NI GT-305-NI
ATI-305-P GTS-305-PI GT-305-PI
ATO-305-N GTS-305-NE GT-305-NE
ATO-305-P GTS-305-PE GT-305-PE
ATI-505-N GTS-505-NI GT-505-NI
ATI-505-P GTS-505-PI GT-505-PI
ATO-505-N GTS-505-NE GT-505-NE
ATO-505-P GTS-505-PE GT-505-PE
ATI-705-N GTS-705-NI GT-705-NI
ATI-705-P GTS-705-PI GT-705-PI
ATO-705-N GTS-705-NE GT-705-NE
ATO-705-P GTS-705-PE GT-705-PE
ATI-705A-N GTS-705-NIA AGT-705-NI
ATI-705A-P GTS-705-PIA AGT-705-PI
ATO-705A-N GTS-705-NEA AGT-705-NE
ATO-705A-P GTS-705-PEA AGT-705-PE
PRINTED 0709 316437-001
Table of Contents
General Information................................................3-5
Specifications.........................................................6, 7
Schematic Diagrams..............................................8, 9
Fault Isolation..................................................... 10-12
Electrical Diagnostic Points
305e/o, 305i, 505e/o 505i ................................13, 14
705e/o (ASME), 705i (ASME) .........................15, 16
Wire Diagrams
305e/o, 305i, 505e/o, 505i .....................................17
705e/o (ASME), 705i (ASME) ...............................18
Flushing the Heat Exchanger .................................19
Component Replacement Instructions
Gas Control Assembly
305e/o, 305i, 505e/o, 505i ...............................20, 21
705e/o (ASME), 705i (ASME) ..........................22, 23
PC Board
305e/o, 305i, 505e, 505i ................................. 27, 28
705e/o (ASME ), 705i (ASME) ............................. 29
Water Flow Control Assembly
305e, 305i, 505e, 505i .................................... 30, 31
505e, 505i ....................................................... 32, 33
705e/o (ASME), 705i (ASME) .............................. 34
Heat Exchanger
305e .................................................................35-37
505e /o.............................................................. 38-40
305i ..................................................................41-44
505i .................................................................. 45-49
705e/o (ASME)................................................. 50-51
705i (ASME) .................................................... 52-54
Fan
505e/o, 305e/o.......................................................24
305i, 505i ...............................................................25
705e/o (ASME), 705i (ASME) ...............................26
Key to Trade Names in this Manual:
(ASME) Indicates that the ASME
(N) Indicates Natural Gas.
(P) Indicates Propane Gas.
(e) Indicates Outdoor Models.
(i) Indicates Indoor Models.
(o) Indicates Outdoor Models.
Gas Pressure Setting Procedure..................... 55, 56
Manifold Pressure Settings.................................... 57
Dip Switches............................................................ 58
models are included.
On-Demand Gas Tankless Water Heater Service Manual
2
Safety Definitions
This is the safety alert symbol. This symbol alerts you to potential hazards that can kill or hurt you and
others.
General Information
DANGER
WARNING
CAUTION
Indicates an imminently hazardous situation which, if not avoided, will result in death or
serious injury.
Indicates a potentially hazardous situation which, if not avoided, could result in death or
serious injury.
Indicates a potentially hazardous situation which, if not avoided, could result in minor or
moderate injury. It may also be used to alert against unsafe practices.
Using this Manual
Repairs should be performed by a qualified service technician.
The following information can be referenced for additional information.
• Operation and Installation Manual
• Hot Water System Design Manual
• Technical Sheets
• Technical Bulletins
Technical Support
Visit the brand website for additional support including contact information for our Technical Service Department.
Recommended Tools
• Volt/Ohm/Amp meter with test probes
• Digital manometer or U tube type manometer with 14 inch water column (W.C.) scale, a hose and two 1/8 inch
taps
• assorted wrenches including a 3/16 Allen wrench
• assorted screw drivers including a long shafted, magnetic tipped screw driver
• leak solution or leak detector
• Teflon tape
WARNING
There are a number of live tests that are required when fault finding this product. Extreme care should be used at
all times to avoid contact with energized components inside the water heater. Before checking for resistance
readings disconnect the power source to the unit and isolate the item from the circuit (unplug it).
CAUTION
Label all wires prior to disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation.
If any of the original wire as supplied with the appliance must
be replaced, it must be replaced with type 18 AWG wire or its
equivalent.
On-Demand Gas Tankless Water Heater Service Manual
3
General Information
Service Information
The on-demand water heaters must be installed according to all local and state codes or, in the absence
of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1 (NFPA 54) - current edition.
CSA American, Inc. National Fire Protection Association
8501 East Pleasat Valley Road 1 Batterymarch Park
Cleveland, OH 44131 Quincy, MA 02269
Check your phone listings for the local authorities having jurisdiction over your installation.
Massachusetts code requires this water heater to be installed in accordance with Massachusetts Plumbing
and Fuel Gas Code 248 CMR Section 2.00 and 5.00.
NOTE: This water heater must be installed according to all local and state codes or, in the absence
of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1(NFPA 54)-current edition.
Water Temperature Regulation
For systems with storage tanks, the water
temperature in certain situation may vary up
to 30°F (16.7°C) higher or lower at the point
of use such as, bathtubs,showers, sink, etc.
HOTTER WATER CAN SCALD: Water heaters, are intended to produce hot water. Water
heated to a temperature which will satisfy
space heating, clothes washing, dish washing, and other sanitizing needs can scald and
permanently injure you upon contact. Some
people are more likely to be permanently injured by hot water than others. These include
the elderly, children, the infirm, or physically/
mentally handicapped. If anyone using hot
water in the home fits into one of these
groups or if there is a local code or state law
requiring a certain temperature water at the
hot water tap, then you must take special
precautions.
Water temperature over 125°F can cause
severe burns instantly or death from scalds.
Children, disabled and elderly are at highest
risk of being scalded.
Feel water before bathing or showering.
Temperature limiting valves are available.
WARNING
In addition to using the lowest possible temperature setting that satisfies your hot water needs, a means
such as a mixing valve, should be used at hot water taps used by these people or at the water heater.
Mixing valves are available at plumbing supply or hardware stores. Follow manufacturer’s instructions for
installation of the valves. Before changing the factory setting on the thermostat see Table “A”. Using the
lowest hot water temperature that meets your needs will also provide the most energy efficient operation
of the water heater.
Never allow small children to use a hot water
tap, or to draw their own bath water. Never
leave a child or handicapped person unattended in a bathtub or shower.
NOTE: A water temperature range of 120
°F (49°C-60°C) is recommended by most
140
dishwasher manufacturers.
°F -
Temperature
Settings
160°F (71°C)
150°F (66°C) About 1-1/2 seconds
140°F (60°C) Less than 5 seconds
130°F (54°C) About 30 seconds
120°F (49°C) More than 5 minutes
80°F (27°C) - - - - - - - - - - - - - - - -
Time to Produce 2nd & 3rd
Degree Burns on Adult Skin
About 1/2 second
Table “A”
On-Demand Gas Tankless Water Heater Service Manual
4
General Information
Closed System/Thermal Expansion
CAUTION - PROPERTY DAMAGE HAZARD
As water is heated, it expands (thermal expansion). In a closed system, the volume of water
will grow. As the volume of water grows, there
will be a corresponding increase in water pressure due to thermal expansion. Thermal expansion can cause premature tank failure (leakage).
This type of failure is not covered under the
limited warranty. Thermal expansion can also
cause intermittent temperature-pressure relief
valve operation: water discharged from the valve
due to excessive pressure build up. The temperature / pressure relief valve is not intended for
the constant relief of thermal expansion. This
condition is not covered under the limited warranty.
A properly-sized thermal expansion tank should
be installed on all closed systems to control the
harmful effects of thermal expansion. Contact a
local plumbing service agency to have a thermal
expansion tank installed.
Figure 1a
Typical water piping installation
Hot Water Return Line
Hot Water
Outlet
Storage
Tank
1“ Min.
Metal Drain
Pan 1-3/4”
Depth Max.
In a closed system use a
thermal expansion tank
Cold Water
Inlet Valve
Cold Water Supply
to Fixture
Temperature and
Pressure Relief Valve
Drain line 3/4”
ID Min.
Drain
Pressure Reducing
Valve with Bypass
Main Water
Supply
Discharge line
6” Max. above drain
Massachusetts:
Install a vacuum relief
in cold water line per
section 19 MGL 142
Temperature and Pressure
Relief Valve
For protection against excessive pressures and
temperatures, a temperature and pressure relief
valve must be installed in the opening on the
on-demand storage tank. This valve must be
design certified by a nationally recognized testing
laboratory that maintains periodic inspection of
the production of listed equipment or materials
as meeting the requirements for Releif Valves for
Hot Water Supply Systems, ANSI Z21.22. The
function of the temperature and pressure relief
valve is to discharge water in large quantities in
the event of excessive temperature or pressure
developing in the water heater. The valve’s relief
pressure must not exceed the working pressure
the water heater as stated on the data plate.
IMPORTANT: Only a new temperature and
pressure relief valve should be used with your
water heater.Do not use an old or existing valve
as it may be damaged or not adequate for the
working pressure of the new water heater.
Do not place any valve between the relief valve
and the tank.
WARNING
Explosion Hazard
If the temperature and pressure relief valve
is dripping or leaking, have a qualified
service technician replace it.
Examples of a qualified service technician
include: Licensed plumbers, authorized gas
company personnel, and authorized service
personnel.
Do not plug valve.
Do not remove valve.
Failure to follow these instructions can
result in death, or explosion.
On-Demand Gas Tankless Water Heater Service Manual
5
Indoor (i)
Specifications
Residential Series
100/101*
Model Number
305
505
705/705 ASME
15,000 - 199,000 NG
15,000 - 190,000 LP
15,000 - 199,000 NG
15,000 - 190,000 LP
19,000 - 237,000
NG & LP
Outdoor (e/o)
Model Number
305
505
705/705 ASME
15,000 - 199,000
NG & LP
15,000 - 199,000
NG & LP
19,000 - 237,000
NG & LP
Input
Min. - Max.
(BTU)
Input
Min. - Max.
(BTU)
Flow Rate
0.6 - 5.3 GPM
(2.3 - 20.1 LPM)
0.6 - 8.5 GPM
(2.3 - 32.0 LPM)
0.6 - 9.8 GPM
(2.3 - 37 LPM)
Flow Rate
0.6 - 5.3 GPM
(2.3 - 20.1 LPM)
0.6 - 8.5 GPM
(2.3 - 32.0 LPM)
0.6 - 9.8 GPM
(2.3 - 37 LPM)
Hot water capacity
@ 45°F Temp. Rise
5.3 GPM (20.1 LPM)
7.4 GPM (28 LPM) NG
7.1 GPM (27 LPM) LP
8.8 GPM (33.3 LPM)
Hot water capacity
@ 45°F Temp. Rise
5.3 GPM (20.1 LPM)
7.3 GPM (27.6 LPM)
8.7 GPM (32.9 LPM)
Efficiency
Rating
84%
84%
84%
Efficiency
Rating
83%
83%
83%
Temperature Range
98 -140° F (37 - 60° C) [1]
98 -140° F (37 - 60° C) [2]
98 -140° F (37 - 60° C) [2]
Temperature Range
98 -140° F (37 - 60° C) [1]
98 -140° F (37 - 60° C) [2]
98 -140° F (37 - 60° C) [2]
NOTE:
[1] Minimum activation flow is approximately 0.6 gallons/minute (2.3 liters/min). Max temperature is 160° (71° C)
with the commercial controller for commercial and hydronic applications only.
[2] Max temperature is 185 ºF (85 ºC) with the commercial controller for commercial and hydronic applications only.
*100 Series is Natural Gas
*101 Series is Propane Gas
On-Demand Gas Tankless Water Heater Service Manual
6
Indoor (i)
Specifications
Residential Series
200/201*
Model Number
305
505
15,000 - 199,000 NG
15,000 - 190,000 LP
Outdoor (e/o)
Model Number
305
505
Input
Min. - Max.
(BTU)
15,000 - 180,000
NG & LP
Input
Min. - Max.
(BTU)
15,000 - 180,000
NG & LP
15,000 - 199,000
NG & LP
Flow Rate
0.6 - 7.5 GPM
(2.3 - 28.4 LPM)
0.6 - 9.4 GPM
(2.3 - 35.5 LPM)
Flow Rate
0.6 - 7.5 GPM
(2.3 - 28.4 LPM)
0.6 - 9.4 GPM
(2.3 - 35.5 LPM)
Hot water capacity
@ 45°F Temp. Rise
6.6 GPM (25.0 LPM)
7.4 GPM (28.0 LPM) NG
7.1 GPM (26.9 LPM) LP
Hot water capacity
@ 45°F Temp. Rise
6.6 GPM (25.0 LPM)
7.4 GPM (28.0 LPM)
Efficiency
Rating
84%
84%
Efficiency
Rating
83%
83%
Temperature Range
98 -140° F (37 - 60° C) [1]
98 -140° F (37 - 60° C) [2]
Temperature Range
98 -140° F (37 - 60° C) [1]
98 -140° F (37 - 60° C) [2]
NOTE:
[1] Minimum activation flow is approximately 0.6 gallons/minute (2.3 liters/min). Max temperature is 160° (71° C)
with the commercial controller for commercial and hydronic applications only.
[2] Max temperature is 185 ºF (85 ºC) with the commercial controller for commercial and hydronic applications only.
*200 Series is Natural Gas
*201 Series is Propane Gas
On-Demand Gas Tankless Water Heater Service Manual
7
(NOT PRESENT ON
ALL MODELS)
Schematic Diagrams
Outdoor Model
(NOT PRESENT ON
ALL MODELS)
(LOCATED ON BRACKET NEAR
FAN ON SOME MODELS)
On-Demand Gas Tankless Water Heater Service Manual
8
(NOT PRESENT ON
ALL MODELS)
Schematic Diagrams
Indoor Model
(NOT PRESENT ON
ALL MODELS)
(LOCATED ON BRACKET NEAR
FAN ON SOME MODELS)
On-Demand Gas Tankless Water Heater Service Manual
9
Fault Isolation
The On-Demand water heater has the ability to check its own operation continuously. If a fault occurs, an error
code will flash on the display of the remote controller. This assists with diagnosing the fault and may enable
you to overcome a problem without a service call.
WARNING
Some of the checks below may need to be done by a qualified service technician. Call a
service technician for any remedy that involves gas or electricity. Call a service
technician if you have any doubt or reservation about performing the remedy yourself.
Accessing Operating Information
Standard and Commercial Controllers
To display the most recent error codes press and hold the “On/Off” button for 2 seconds. While holding the “On/
Off” button press the ▲ button. The last 9 error codes will flash one after the other. To exit this mode press the
“On/Off” and ▲ button as before.
To display the water flow through the water heater press and hold the ▲ button for 2 seconds and without
releasing the ▲ button press the “On/Off” button.
To display the outlet water temperature press and hold the ▼ button for 2 seconds and without releasing the ▼
button press the “On/Off” button.
Operation
1. Water Flow Begins.
• Water Flow Sensor sends pulses to the PC
Board.
• PC Board senses flow greater than 0.6 GPM
(approximate).
• Firing Sequence begins.
2. Firing Sequence.
• PC Board monitors inlet/outlet water
temperature, temperature set point, and water
flow rate.
• Combustion fan energized. Purges combustion
chamber.
• Spark igniter begins sparking.
• Gas control valve opens to minimum fire rate.
• Flame rod proves ignition.
• Spark igniter stops sparking.
3. Normal Operation.
• PC Board monitors flame rod, fan motor
frequency, outlet water temperature, controller
temperature set point and water flow rate.
• Gas control valve modulates gas input to
required firing rate.
• Combustion fan speed is adjusted for the
required firing rate.
• Water flow control valve is adjusted as needed.
4. Shut-down Sequence.
• PC Board senses flow rate less than 0.5 gpm
(approximate).
• Gas control valve closes.
• Water flow control valve resets to standby
position.
• Combustion fan runs for a short period of time
at low speed.
5. Standby Mode.
• PC Board monitors water temperature and
remote controls.
• Freeze protection is activated as needed.
On-Demand Gas Tankless Water Heater Service Manual
10
Fault Isolation
Code Fault Remedy
02
No burner operation during
freeze protection mode
Service Call - Check for possible freeze damage to heat exchanger.
10
11
12
Air Supply or Exhaust
Blockage
No Ignition Check that the gas is turned on at the water heater, gas meter, or cylinder.
Flame Failure Check that the gas is turned on at the water heater and gas meter. Check for
Ensure approved venting materials are being used.
Check that nothing is blocking the flue inlet or exhaust.
Check all vent components for proper connections.
Ensure vent length is within limits.
Ensure condensation collar was installed correctly.
Verify dip switches are set properly.
Check fan for blockage.
Ensure gas type and pressure is correct.
Ensure gas line, meter, and/or regulator is sized properly.
Bleed all air from gas lines.
Verify dip s
Ensure appliance is properly grounded.
Disconnect 2-Unit or Multi-Unit connections to isolate the problem.
Ensure igniter is operational.
Check igniter wiring harness for damage.
Check gas solenoid valves for open or short circuits.
Remove burner cover and ensure all burners are properly seated.
Remove burner plate and inspect burner surface for condensation or debris.
obstructions in the flue outlet.
Ensure gas line, meter, and/or regulator is sized properly.
Ensure gas type and pressure is correct.
Bleed all air from gas lines.
Ensure proper venting material was installed.
Ensure condensation collar was installed properly.
Ensure vent length is within limits.
Verify dip switches are set properly.
Ensure appliance is properly grounded.
Disconnect keypad.
Disconnect all 2-Unit or Multi-Unit connections to isolate the problem.
Check power supply for loose connections.
Check power supply for proper voltage and voltage drops.
Ensure flame rod wire is connected.
Remove flame rod and check for carbon build-up; clean with sand paper or emery
cloth.
Disconnect and reconnect all wiring harnesses on unit and PC board.
Check all components for electrical short.
Check gas solenoid valves for open or short circuits.
Remove burner plate and inspect burner surface for condensation or debris.
witches are set properly.
On-Demand Gas Tankless Water Heater Service Manual
11
Code Fault Remedy
Fault Isolation
14
16
32
33
34
52
61
65
71
72
LC
No
code
Thermal Fuse Check gas type of unit and ensure it matches gas type being used.
Check for restrictions in air flow around unit and vent terminal.
Check for low water flow in a circulating system causing short-cycling.
Ensure dip switches are set to the proper position.
Check for foreign materials in combustion chamber and/or exhaust piping.
Check heat exchanger for cracks and/or separations.
Check heat exchanger surface for hot spots which indicate blockage due to scale build-
up. Refer to instructions in manual for flushing heat exchanger.
Measure resistance of safety circuit.
Ensure high fire and low fire manifold pressure is correct.
Check for improper conversion of product.
Over Temperature
Warning
Outgoing Water
Temperature Sensor
Fault
Heat Exchanger
Outgoing Temperature
Sensor Fault
Combustion Air
Temperature Sensor
ault
F
Modulating Solenoid
Valve Signal Abnormal
Combustion Fan
Failure
Water Flow Control
Fault
SV0, SV1, SV2, and
SV3 Solenoid Valve
Circuit Fault
Flame Sensing Device
Fault
Scale Build-up in Heat
Exchanger (when
checking maintenance
code history, “00” is
substituted for “LC”)
Nothing happens when
water flow is activated.
Check for restrictions in air flow around unit and vent terminal.
Check for low water flow in a circulating system causing short-cycling.
Check for foreign materials in combustion chamber and/or exhaust piping.
Check for clogged heat exchanger.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
Check for restrictions in air flow around unit and vent terminal.
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Ensure fan blade is tight on motor shaft and is in good condition.
Replace sensor.
Check modulating gas solenoid valve wiring harness for loose or damaged terminals.
Measure resistance of valve coil.
Ensure fan will turn freely.
Check wiring harness to motor for damaged and/or loose connections.
Measure resistance of motor winding.
The water flow control valve has failed to close during the bath fill function. Immediately
turn off the water and discontinue the bath fill function. Contact a state qualified or
licensed contractor to service the appliance.
Check wiring harness to all solenoids for damage and/or loose connections.
Measure resistance of each solenoid valve coil.
Ensure flame rod is touching flame when unit fires.
Check all wiring to flame rod for damage.
Remove flame rod and check for carbon build-up; clean with sand paper or emery cloth.
Check inside burner chamber for any foreign material blocking flame at flame rod.
Measure micro amp output of sensor circuit with flame present.
Replace flame rod.
Flush heat exchanger. Refer to instructions in manual.
Replace heat exchanger.
NOTE: The LC code is the only code that will allow the unit to keep running. The
display will alternate between the LC code and the temperature setting. The controller
will continue to beep. The LC code will reset if power is turned off and then on.
Clean inlet water supply filter, see page 19 step 12 for cleaning instructions.
On new installations ensure hot and cold water
Check for bleed over. Isolate unit from building by turning off hot water line to building.
Isolate the circulating system if present. Open your pressure relief valve; if water is
flowing, there is bleed over in your plumbing.
Ensure you have at least the minimum flow rate required to fire unit.
Ensure turbine spins freely.
Measure the resistance of the water flow control sensor.
lines are not reversed.
On-Demand Gas Tankless Water Heater Service Manual
12
Electrical Diagnostic Points
305e/o, 305i, 505e/o, 505i
Wire Color Voltage Resistance Connector No. Pin No.’s
(SV1, SV2, SV3, POV) Gas Valve and Modulating Solenoids
(Main) Pink - Black
11 - 13 VDC 36.8 - 44.8 ohms
(POV) Pink - Pink 2 - 15 VDC 67 - 81 ohms H3 9 ~ 10
(M) Water Flow Servo
Red - Blue 11 - 13 VDC 22 - 26 ohms F7 9 ~ 10
Gray - Brown 4 - 6 VDC N/A F7 5 ~ 7
Gray - Yellow N/A N/A F7 5 ~ 8
NOTE: At the F connector on the PCB: gray wire turns to black, orange wire turns to red
(QS) Water Flow Sensor
Black - Red 11 - 13 VDC 5.5 - 6.2 K ohms F2 1 ~ 3
Yellow - Black 4 - 7 VDC 1 -
Bypass Flow Control (only on 505e/o and 505i)
Brown - White
2 - 6 VDC
(unit in operating
mode)
1.4 mega ohms F2 2 ~ 3
15 - 35 K ohms G1
H5 6 ~ 7
6 ~ 5 6H wolleY - kcalB )1VS(
6 ~ 4 7H eulB - kcalB )2VS(
6 ~ 3 8H nworB - kcalB )3VS(
1 ~ 5
5 ~ 2 etihW - egnarO
5 ~ 3 etihW - wolleY
5 ~ 4 dnuorG/etihW - deR
(IG) Ignition System
Gray - Gray 90 - 110 VAC N/A C1 1 ~ 2
(FM) Combustion Fan Motor
Red - Black 6 - 45 VDC N/A E1 1 ~ 2
White - Black 5 - 10 VDC 9.2 - 9.4 K ohms E1 2 ~ 4
Yellow - Black 11 ~ 13 VDC 3.5 - 3.9 K ohms E1 2 ~ 3
With the meter set on hertz scale, 60-420 hertz should be across the red and yellow wires at
terminals 2 and 4.
On-Demand Gas Tankless Water Heater Service Manual
13
Electrical Diagnostic Points
305e/o, 305i, 505e/o, 505i
Wire Color Voltage Resistance Connector No. Pin No.’s
Thermal Fuse / Overheat Switch
Red - Red 11 - 13 VDC below 1 ohm F6 H1 F6 ~ H12
Flame Rod
Place one lead of the meter to the flame rod and the other to ground. With the unit running, 5-150
VAC should be read. Set the meter to the μ amp scale and series the meter in line with the flame
rod. Proper flame circuit should read 1 μ amp or greater. If not, then remove the flame rod and
check for carbon and damage.
Thermistors
Check all thermistors by inserting meter leads into each end of the thermistor plug. Set the meter to
the 20 K ohm scale and read resistance. Applying heat to the thermistor bulb should decrease the
resistance. Applying ice to the thermistor bulb should increase the resistance. Typical resistance
values are:
for 140°F; 0.6-0.8 K ohm for 221°F
Outgoing Water Thermistor
11.4-14 K ohm for 59°F; 6.4-7.8 K ohm for 86°F; 3.6-4.5 K ohm for 113°F; 2.2-2.7 K ohm
Heat Exchanger Temperature Thermistor
Intake Air Thermistor
oba ees etihW - egnarO
Surge Protector
Black - White 108 - 132 VAC N/A D2 1 ~ 3
Blue - Brown 108 - 132 VAC N/A D1 1 ~ 3
With the power off, check the continuity through the surge protector. Check by placing one meter
lead on the top pin #1 and bottom pin #3. Check by placing one meter lead on the top pin #3 and
bottom pin #1. If there is continuity across both sets of points, then the surge protector is good.
Controller
Terminals B1
Frost Protection
There are electrical heating elements mounted at different points to protect the water heater from
freezing.
heaters located on the hot water outlet line 180 - 207 ohms
heater located on heat exchanger piping 156 - 180 ohms
10 - 13 VDC 1.5 - 3.0 K ohms B 1 ~ 3
4 ~ 3 5F evoba ees etihW - etihW
11 ~ 3 4F evoba ees etihW - kniP
21 ~ 3 3F ev
heater located on water flow sensor 24 - 28 ohms
Amp fuses
There are two inline 3 amp glass fuses. Remove the fuse and check continuity through it. If there is
continuity then the fuse is good.
On-Demand Gas Tankless Water Heater Service Manual
14
Electrical Diagnostic Points
705e/o (ASME),
705i (ASME)
Wire Color Voltage Resistance Connector No. Pin No.’s
(SV1, SV2, SV3, POV) Gas Valve and Modulating Solenoids
(Main) Pink - Black
11 - 13 VDC
(POV) Orange - Orange 2 - 15 VDC 67 - 81 ohms H2 9 ~ 10
(M) Water Flow Servo
Red - Blue 11 - 13 VDC 22 - 28 ohms F5 9 ~ 10
Gray - Brown 4 - 6 VDC N/A F5 5 ~ 7
Gray - Yellow N/A N/A F5 5 ~ 8
NOTE: At the F connector on the PCB: gray wire turns to black
(QS) Water Flow Sensor
Black - Red 11 - 13 VDC 5.5 - 6.2 K ohms F2 1 ~ 3
Yellow - Black 4 - 7 VDC 1 - 1.4 mega ohms F
Bypass Flow Control
Brown - White
2 - 6 VDC
(unit in operating
mode)
24 - 28 ohms H3 6 ~ 7
37 - 43 ohms
37 - 43 ohms
37 - 43 ohms
2 2 ~ 3
1 ~ 5
15 - 35 K ohms G1
6 ~ 5 4H deR - kcalB )1VS(
6 ~ 4 5H egnarO - kcalB )2VS(
6 ~ 3 6H wolleY - kcalB )3VS(
5 ~ 2 etihW - egnarO
5 ~ 3 etihW - wolleY
5 ~ 4 dnuorG/etihW - deR
(IG) Ignition System
Gray - Gray 90 - 110 VAC N/A C1 1 ~ 2
(FM) Combustion Fan Motor
Red - Black 6 - 45 VDC N/A E1 1 ~ 2
White - Black 5 - 10 VDC 9.2 - 9.4 K ohms E1 2 ~ 4
Yellow - Black 11 ~ 13 VDC 3.5 - 3.9 K ohms E1 2 ~ 3
With the meter set on hertz scale, 60-420 hertz should be across the red and yellow wires at
terminals 2 and 4.
On-Demand Gas Tankless Water Heater Service Manual
15
Electrical Diagnostic Points
705e/o (ASME),
705i (ASME)
Wire Color Voltage Resistance Connector No. Pin No.’s
Thermal Fuse / Overheat Switch
Red - White 11 - 13 VDC below 1 ohm F6 H1 F6 ~ H12
Flame Rod
Place one lead of the meter to the flame rod and the other to ground. With the unit running, 5-150
VAC should be read. Set the meter to the μ amp scale and series the meter in line with the flame
rod. Proper flame circuit should read 1 μ amp or greater. If not, then remove the flame rod and
check for carbon and damage.
Thermistors
Check all thermistors by inserting meter leads into each end of the thermistor plug. Set the meter to
the 20 K ohm scale and read resistance. Applying heat to the thermistor bulb should decrease the
resistance. Applying ice to the thermistor bulb should increase the resistance. Typical resistance
values are:
for 140°F; 0.6-0.8 K ohm for 221°F
Outgoing Water Thermistor
11.4-14 K ohm for 59°F; 6.4-7.8 K ohm for 86°F; 3.6-4.5 K ohm for 113°F; 2.2-2.7 K ohm
Heat Exchanger Temperature Thermistor
Surge Protector
Black - White 108 - 132 VAC N/A D2 1 ~ 3
Blue - Brown 108 - 132 VAC N/A D1 1 ~ 3
With the power off, check the continuity through the surge protector. Check by placing one meter
lead on the top pin #1 and bottom pin #3. Check by placing one meter lead on the top pin #3 and
bottom pin #1. If there is continuity across both sets of points, then the surge protector is good.
Controller
Terminals B1 10 - 13 VDC 1.5 - 3.0 K ohms B 1 ~ 3
Frost Protection
There
are electrical heating elements mounted at different points to protect the water heater from
freezing. Voltage through this circuit should be 120 VAC.
heater located on the hot water outlet line 180 - 207 ohms
heater located on heat exchanger piping 156 - 180 ohms
heater located on water flow sensor 24 - 28 ohms
Amp fuses
4 ~ 3 4F evoba ees etihW - etihW
11 ~ 3 3F evoba ees etihW - kniP
There are two inline 3 amp glass fuses. Remove the fuse and check continuity through it. If there is
continuity then the fuse is good.
On-Demand Gas Tankless Water Heater Service Manual
16
Wiring Diagram
BY-PASS SERVO MODEL ONLY
BY-PASS FLOW
CONTROL DEVICE
FREEZE PROTECTION
OPTION
WATER FLOW
SENSOR
QS
BK
F
2
RR
Y
Y
BK
INDOOR MODEL ONLY
AIR TEMPERATURE
THERMISTOR
HEAT EXCHANGER
THERMISTOR
OUTGOING WATER
THERMISTOR
F
7
BL
BR
GY
W
W
W
W
W
W
R
Y
WATER FLOW
CONTROL DEVICE
COMBUSTION FAN
THERMAL FUSES
H
2
OVERHEAT
SWITCH
305e/o, 305i, 505e/o, 505i
COLOR CODING
G
1
BR
O
Y
R
W
G
R
F
1
F
3
W
O
F
4
W
P
F
5
W
W
GY
R
BL
Y
BR
FM
W
Y
BK
R
F
6
R
R
R
R
H
1
E
1
O
13
P
5
R
BL BR
Y
(CN12)
BRROYW
G
1
(CN7)
F
YBKR
G
1
(CN5)
WW
E
41
YBKR
W
A
3
(CN9)
H
(CN2 )
12 1
P
YP
R
BLBKP
MAX
MIN
BKRW
Dip SW1
O
1
F
F
Dip SW2
O
F
F
B
1
YBR
(CN1)
3
C
for REU-EZC
(Optional)
MODULATING VALVE
CURRENT ADJUSTING
1
2
3
4
5
6
7
Gas pressure
8
1
Gas type
2
3
Spare Parts Only
4
5
6
B
BK
BK
C
1
GY
GY
(CN4)
1
GY
GY
IGNITER
W :White
BK:Black
BR:Brown
R :Red
BL:Blue
Y :Yellow
P :Pink
O :Orange
G :Green
GY:Gray
REMOTE CO NTROLLER
SPARK
ELECTRODE
IG
GND
MODULATING
SOLENOID VALVE
FLAME ROD
MAIN SOLENOID VALVE
SOLENOID VALVE 1
SOLENOID VALVE 2
SOLENOID VALVE 3
H
POV
H
3
P
P
Y
4
H
5
P
SV0
BK
H
SV1
SV2
SV3
6
Y
BK
H
7
BL
BK
H
8
BR
BK
G/Y
GND
SURGE
PROTECTOR
1
BL
3
BR
D
1
G/Y
GND
D
2
BK
3
1
W
(CN3)
BL
BR
BKW
D
FUSE
(3A)
1
3
W
W
AC120VAC120V
HOT
HOT
NEUTRAL
NEUTRAL
GROUND
On-Demand Gas Tankless Water Heater Service Manual
17
D
3
FROST SENSING
SWITCH
BLBL
(W) (W)
BLBL
ANTI-FROST HEATER
D
5
ANTI-FROST HEATER
D
4
Wiring Diagram
705e/o (ASME),
705i (ASME)
BL:Blue
BKRW
Dip SW1
BR:Brown
1
O
A
F
YBKR
G
Y :Yellow
P :Pink
O :Orange
R :Red
2
3
F
F
1
GY:Gray
G :Green
REMOTE CONTROLLER
1
Gas pressure
Gas type
87654
123
F
O
Dip SW2
B
Spare Parts Only
5
4
F
BK
6
3
B
H
3
(CN9 )
(CN2 )
(CN5)
1
WW
BR
Y
BL
R
P
12 1
E
4 1
W :White
BK:Black
COLOR CODING
for REU-EZC
(Optional)
1
A
MODULATING VALVE
CURRENT ADJUSTING
MIN
MAX
G
(CN7 )
1
BRROYW
5
ANTI-FROST
HEATER
W
W
W
W
W
W
5
4
D
FROST SENSING
W
SWITCH
W
W
BL BL
3
D
W
SPARK
BK
1
1
C
(CN1)
Y
Y
OBK
RP
O
O
W
R
BK
Y
W
(CN12)
6
D
D
W
W
W
W
W
ELECTRODE
GND
IG
GY
GY
IGNITER
1
C
GY
GY
(CN4 )
FUSE
AC120VAC120V
(3A)
2
D
1
WBK
1
D
(CN3)
BK
W
BK
GROUND
NEUTRAL
NEUTRAL
HOT
HOT
1
D
SURGE
PROTECTOR
G/Y
WBK
1
W
3
G/Y
Y
GND
GND
7
H
FLAME ROD
13
O
2
H
R
W
1
6
RBKY
1
G
ORW
BR
BY-PASS FLOW
Y
CONTROL DEVICE
G
FREEZE PROTECTION
R
1
F
RR
2
F
(OPTIONAL)
WATER FLOW
Y
Y
QS
SENSOR
BK
BK
W
W
P
W
GY
4
3
F
F
W
W
WATER THERMISTOR
HEAT EXCHANGER
W
W
R
BL
5
F
WATER THERMISTO R
OUTGOING WATER
Y
BLRBR
BRYGY
W
FM
1
E
COMBUSTION FAN
ATER FLOW
CONTROL DEVICE
H
F
W
R
MODULATING
RR
OVERHEAT
SWITCH
THERMAL FUSES
On-Demand Gas Tankless Water Heater Service Manual
18
O
POV
O
P
R
BK
BK
4
3
H
H
SV1
SV0
Y
BK
SV2
BK
6
H
SV3
5
H
SOLENOID VALVE
(CENTER)
SOLENOID VALVE 1
(LEFT)
SOLENOID VALVE 2
(RIGHT)
SOLENOID VALVE 3
MAIN SOLENOID VALVE
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