A.O. Smith GTS-305-NE User manual

PRINTED 0709 316437-001
On-Demand Gas Tankless
Water Heater Service Manual
Service information for single and multiple unit installations
for residential, commercial, recirculation and storage tank systems.
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
Series 100/101 & Series 200/201
http://waterheatertimer.org/pdf/

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
Fan
505e/o, 305e/o.......................................................24
305i, 505i ...............................................................25
705e/o (ASME), 705i (ASME) ...............................26
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
Gas Pressure Setting Procedure..................... 55, 56
Manifold Pressure Settings.................................... 57
Dip Switches............................................................ 58
On-Demand Gas Tankless Water Heater Service Manual
2
Key to Trade Names in this Manual:
(ASME) Indicates that the ASME models are included.
(N) Indicates Natural Gas.
(P) Indicates Propane Gas.
(e) Indicates Outdoor Models.
(i) Indicates Indoor Models.
(o) Indicates Outdoor Models.

General Information
Safety Definitions
This is the safety alert symbol. This symbol alerts you to potential hazards that can kill or hurt you and
others.
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.
DANGER
CAUTION
WARNING
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
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.
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).
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.
Label all wires prior to disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation.
CAUTION
On-Demand Gas Tankless Water Heater Service Manual
3

General Information
On-Demand Gas Tankless Water Heater Service Manual
4
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.
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 heat-
ers, are intended to produce hot water. Water
heated to a temperature which will satisfy
space heating, clothes washing, dish wash-
ing, and other sanitizing needs can scald and
permanently injure you upon contact. Some
people are more likely to be permanently in-
jured 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
Temperature
Settings
Time to Produce 2nd & 3rd
Degree Burns on Adult Skin
160°F (71°C) About 1/2 second
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) - - - - - - - - - - - - - - - -
Table “A”
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.
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 un-
attended in a bathtub or shower.
NOTE: A water temperature range of 120°F -
140°F (49°C-60°C) is recommended by most
dishwasher manufacturers.

General Information
On-Demand Gas Tankless Water Heater Service Manual
5
Closed System/Thermal Expansion
CAUTION - PROPERTY DAMAGE HAZARD
As water is heated, it expands (thermal expan-
sion). In a closed system, the volume of water
will grow. As the volume of water grows, there
will be a corresponding increase in water pres-
sure due to thermal expansion. Thermal expan-
sion 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 temper-
ature / pressure relief valve is not intended for
the constant relief of thermal expansion. This
condition is not covered under the limited war-
ranty.
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.
Hot Water
Outlet
In a closed system use a
thermal expansion tank
Cold Water
Inlet Valve Pressure Reducing
Valve with Bypass
Main Water
Supply
Cold Water Supply
to Fixture
Temperature and
Pressure Relief Valve
Discharge line
6” Max. above drain
Drain line 3/4”
ID Min.
Drain
1“ Min.
Metal Drain
Pan 1-3/4”
Depth Max.
Massachusetts:
Install a vacuum relief
in cold water line per
section 19 MGL 142
Figure 1a
Typical water piping installation
Storage
Tank
Hot Water Return Line
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.
WARNING
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.

Specifications
Model Number Temperature Range
305 15,000 - 199,000 NG
15,000 - 190,000 LP
705/705 ASME
Indoor (i)
On-Demand Gas Tankless Water Heater Service Manual
6
Input
Min. - Max.
(BTU)
Flow Rate Hot water capacity
@ 45°F Temp. Rise
0.6 - 5.3 GPM
(2.3 - 20.1 LPM) 5.3 GPM (20.1 LPM)
Efficiency
Rating
84%
505 15,000 - 199,000 NG
15,000 - 190,000 LP
0.6 - 8.5 GPM
(2.3 - 32.0 LPM)
7.4 GPM (28 LPM) NG
7.1 GPM (27 LPM) LP
98 -140°F (37 - 60°C) [1]
84% 98 -140°F (37 - 60°C) [2]
98 -140°F (37 - 60°C) [2]
84%
8.8 GPM (33.3 LPM)
19,000 - 237,000
NG & LP
0.6 - 9.8 GPM
(2.3 - 37 LPM)
Model Number Temperature Range
305 15,000 - 199,000
NG & LP
705/705 ASME
Outdoor (e/o)
Input
Min. - Max.
(BTU)
Flow Rate Hot water capacity
@ 45°F Temp. Rise
0.6 - 5.3 GPM
(2.3 - 20.1 LPM) 5.3 GPM (20.1 LPM)
Efficiency
Rating
83%
505 0.6 - 8.5 GPM
(2.3 - 32.0 LPM) 7.3 GPM (27.6 LPM)
98 -140°F (37 - 60°C) [1]
83% 98 -140°F (37 - 60°C) [2]
98 -140°F (37 - 60°C) [2]
83%
8.7 GPM (32.9 LPM)
19,000 - 237,000
NG & LP
0.6 - 9.8 GPM
(2.3 - 37 LPM)
15,000 - 199,000
NG & LP
Residential Series
100/101*
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

Specifications
Model Number Temperature Range
305
Indoor (i)
On-Demand Gas Tankless Water Heater Service Manual
7
Input
Min. - Max.
(BTU)
Flow Rate Hot water capacity
@ 45°F Temp. Rise
0.6 - 7.5 GPM
(2.3 - 28.4 LPM)
Efficiency
Rating
84%
505 15,000 - 199,000 NG
15,000 - 190,000 LP
0.6 - 9.4 GPM
(2.3 - 35.5 LPM)
98 -140°F (37 - 60°C) [1]
84% 98 -140°F (37 - 60°C) [2]
Model Number Temperature Range
305 15,000 - 180,000
NG & LP
Outdoor (e/o)
Input
Min. - Max.
(BTU)
Flow Rate Hot water capacity
@ 45°F Temp. Rise
0.6 - 7.5 GPM
(2.3 - 28.4 LPM) 6.6 GPM (25.0 LPM)
Efficiency
Rating
83%
505 0.6 - 9.4 GPM
(2.3 - 35.5 LPM) 7.4 GPM (28.0 LPM)
98 -140°F (37 - 60°C) [1]
83% 98 -140°F (37 - 60°C) [2]
15,000 - 199,000
NG & LP
Residential Series
200/201*
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.
6.6 GPM (25.0 LPM)
7.4 GPM (28.0 LPM) NG
15,000 - 180,000
NG & LP
7.1 GPM (26.9 LPM) LP
*200 Series is Natural Gas
*201 Series is Propane Gas

Schematic Diagrams
Outdoor Model
(NOT PRESENT ON
ALL MODELS)
(LOCATED ON BRACKET NEAR
FAN ON SOME MODELS)
(NOT PRESENT ON
ALL MODELS)
On-Demand Gas Tankless Water Heater Service Manual
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Schematic Diagrams
Indoor Model
(NOT PRESENT ON
ALL MODELS)
(NOT PRESENT ON
ALL MODELS)
(LOCATED ON BRACKET NEAR
FAN ON SOME MODELS)
On-Demand Gas Tankless Water Heater Service Manual
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Fault Isolation
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.
WARNING
Accessing Operating Information
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.
Standard and Commercial Controllers
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.
Operation
On-Demand Gas Tankless Water Heater Service Manual
10
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.

Fault Isolation
Code Fault Remedy
02 No burner operation during
freeze protection mode
Service Call - Check for possible freeze damage to heat exchanger.
10 Air Supply or Exhaust
Blockage
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.
11 No Ignition Check that the gas is turned on at the water heater, gas meter, or cylinder.
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 switches are set properly.
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.
12 Flame Failure Check that the gas is turned on at the water heater and gas meter. Check for
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.
On-Demand Gas Tankless Water Heater Service Manual
11

14 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.
16 Over Temperature
Warning
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.
32 Outgoing Water
Temperature Sensor
Fault
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
33 Heat Exchanger
Outgoing Temperature
Sensor Fault
Check sensor wiring for damage.
Measure resistance of sensor.
Clean sensor of scale build-up.
Replace sensor.
34 Combustion Air
Temperature Sensor
Fault
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.
52 Modulating Solenoid
Valve Signal Abnormal
Check modulating gas solenoid valve wiring harness for loose or damaged terminals.
Measure resistance of valve coil.
61 Combustion Fan
Failure
Ensure fan will turn freely.
Check wiring harness to motor for damaged and/or loose connections.
Measure resistance of motor winding.
65 Water Flow Control
Fault
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.
71 SV0, SV1, SV2, and
SV3 Solenoid Valve
Circuit Fault
Check wiring harness to all solenoids for damage and/or loose connections.
Measure resistance of each solenoid valve coil.
72 Flame Sensing Device
Fault
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.
LC Scale Build-up in Heat
Exchanger (when
checking maintenance
code history, “00” is
substituted for “LC”)
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.
No
code
Nothing happens when
water flow is activated.
Clean inlet water supply filter, see page 19 step 12 for cleaning instructions.
On new installations ensure hot and cold water lines are not reversed.
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.
Code Fault Remedy
Fault Isolation
On-Demand Gas Tankless Water Heater Service Manual
12

Electrical Diagnostic Points
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
H5 6 ~ 7
6~56HwolleY-kcalB)1VS(
6~47HeulB-kcalB)2VS(
6~38HnworB-kcalB)3VS(
(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 - 1.4 mega ohms F2 2 ~ 3
Bypass Flow Control (only on 505e/o and 505i)
Brown - White
2 - 6 VDC
(unit in operating
mode)
15 - 35 K ohms G1
1 ~ 5
5~2etihW-egnarO
5~3etihW-wolleY
5~4dnuorG/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
305e/o, 305i, 505e/o, 505i

Electrical Diagnostic Points
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 μamp scale and series the meter in line with the flame
rod. Proper flame circuit should read 1 μamp 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: 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
for 140°F; 0.6-0.8 K ohm for 221°F
Outgoing Water Thermistor
4~35FevobaeesetihW-etihW
Heat Exchanger Temperature Thermistor
11~34FevobaeesetihW-kniP
21~33Fev
obaeesetihW-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 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.
heaters 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
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.
Intake Air Thermistor
On-Demand Gas Tankless Water Heater Service Manual
14
305e/o, 305i, 505e/o, 505i

Electrical Diagnostic Points
Wire Color Voltage Resistance Connector No. Pin No.’s
(SV1, SV2, SV3, POV) Gas Valve and Modulating Solenoids
(Main) Pink - Black
11 - 13 VDC
24 - 28 ohms H3 6 ~ 7
6~54HdeR-kcalB)1VS(
6~45HegnarO-kcalB)2VS(
6~36HwolleY-kcalB)3VS(
(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 F2 2 ~ 3
Bypass Flow Control
Brown - White
2 - 6 VDC
(unit in operating
mode)
15 - 35 K ohms G1
1 ~ 5
5~2etihW-egnarO
5~3etihW-wolleY
5~4dnuorG/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.
37 - 43 ohms
37 - 43 ohms
37 - 43 ohms
On-Demand Gas Tankless Water Heater Service Manual
15
705e/o (ASME),
705i (ASME)

Electrical Diagnostic Points
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 μamp scale and series the meter in line with the flame
rod. Proper flame circuit should read 1 μamp 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: 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
for 140°F; 0.6-0.8 K ohm for 221°F
Outgoing Water Thermistor
4~34FevobaeesetihW-etihW
Heat Exchanger Temperature Thermistor
11~33FevobaeesetihW-kniP
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
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
705e/o (ASME),
705i (ASME)

Wiring Diagram
305e/o, 305i, 505e/o, 505i
COLOR CODING
W :White
BK:Black
BR:Brown
R :Red
BL:Blue
Y :Yellow
P :Pink
O :Orange
G :Green
GY:Gray
1
3
BR
3
1
B
1
2
O
F
F
Dip SW1
3
8
7
6
5
4
F
5
W
W
B
1
BK
BK
MIN
MAX
MODULATING VALVE
CURRENT ADJUSTING
Gas pressure
F
4
W
W
W
P
W
W
OUTGOING WATER
THERMISTOR
HEAT EXCHANGER
THERMISTOR
Y
BR
O
R
W
BRROYW
BKRW
for REU-EZC
(Optional)
1
13
WATER FLOW
SENSOR
BK
F
2
Y
RR
Y
BK
QS
BY-PASS FLOW
CONTROL DEVICE
YBKR
FREEZE PROTECTION
OPTION
G
W
W
W
O
F
3
WW
O
P
BL
R
BR
Y
GY
WATER FLOW
CONTROL DEVICE
R
BL
BR
Y
GY
G
R
AIR TEMPERATURE
THERMISTOR
R
BL BR
Y
INDOOR MODEL ONLY
COMBUSTION FAN
FM R
BK
Y
W
E
1
W
41
YBK R
BY-PASS SERVO MODEL ONLY
1
1
THERMAL FUSES
R
R
OVERHEAT
SWITCH
H
2
H
1
MODULATING
SOLENOID VALVE
POV
H
3
P
P
H
4
Y
FLAME ROD
H
5
SV1
H
7
H
6
SV0
BL
BK
SV2
BK
P
Y
BK
MAIN SOLENOID VALVE
SOLENOID VALVE 1
SOLENOID VALVE 2
F
6
YBR
BLBKP
P
(CN2)
YP
R
12 1
SOLENOID VALVE 3
H
8
BR
BK
SV3
GY
C
1
IG
GY
GY
IGNITER GND
GY
SURGE
PROTECTOR
3
1
BR
BL
G/Y
D
2
W
BK
1
3
GND
FUSE
(3A)
BKW
W
BLBL
D
4
ANTI-FROST HEATER
AC120VAC120V
HOT
NEUTRAL
HOT
NEUTRAL
GROUND
G/Y
D
1
GND
D
5
ANTI-FROST HEATER
BLBL
D
3
FROST SENSING
SWITCH
W
BL
REMOTE CONTROLLER
SPARK
ELECTRODE
5
4
Spare Parts Only
Gas type
1
2
3
O
F
F
Dip SW2
6
A
C
D
E
F
G
H
F
1
G
1
(CN3)
(CN4)
(CN1)
(CN12)
(CN5)
(CN7)
(CN9)
5
3
R
R
F
7
(W) (W)
On-Demand Gas Tankless Water Heater Service Manual
17

Wiring Diagram
705e/o (ASME),
705i (ASME)
A
3 1
W
3
1
B
1 2
O
F F
Dip SW1
3 8
7
6 5 4
F
4
W W
B
1
BK BK
MIN
MAX
MODULATING VALVE CURRENT ADJUSTING
Gas pressure
F
3
W W
W
P W
W
OUTGOING WATER
WATER THERMISTOR
HEAT EXCHANGER
WATER THERMISTOR
Y
BR
O R WBRROYW
BKRW
for REU-EZC (Optional)
1
13
WATER FLOW
SENSOR
BK
F
2
Y RR
Y
BK
QS
BY-PASS FLOW
CONTROL DEVICE
YBKR
FREEZE PROTECTION
(OPTIONAL)
G
WW
P
BL
R
BR
Y
GY
W
ATER FLOW
CONTROL DEVICE
R
BL BR
Y
GY
G R
R
BL BR
Y
COMBUSTION FAN
FM
R
BK
Y W
E
1
W
4 1
YBKR
1
1
MODULATING
SOLENOID VALVE
POV
H
2
O O
H
7
Y
FLAME ROD
H
3
SV1
H
5
H
4
SV0
O
BK
SV2
BK
P R
BK
MAIN SOLENOID VALVE
SOLENOID VALVE 1
(CENTER)
SOLENOID VALVE 2
(LEFT)
Y
Y
OBK
O
O
(CN2)
RP
W
12 1
SOLENOID VALVE 3
(RIGHT)
H
6
Y
BK
SV3
GY
C
1
IG
GY GY
IGNITER GND
GY
FUSE (3A)
BK
W
AC120VAC120V
HOT
NEUTRAL
HOT
NEUTRAL
GROUND
GND
BK
REMOTE CONTROLLER
SPARK
ELECTRODE
5 4
Spare Parts Only
Gas type
1 2 3
O
F F
Dip SW2
6
C
D
E
F
G
H
F
1
G
1
(CN3)
(CN4)
(CN1)
(CN12)
(CN5)
(CN7)
(CN9)
5
3
D
2
D
1
1
WBK
WBK
G/Y
SURGE PROTECTOR
GND
R
W
RR
H
1
F
6
THERMAL FUSES
OVERHEAT SWITCH
R W
COLOR CODING
W :White BK:Black BR:Brown
R :Red
BL:Blue Y :Yellow
P :Pink O :Orange
G :Green
GY:Gray
BL BL
W
W W W W
W
ANTI-FROST HEATER
D
5
D
3
FROST SENSING SWITCH
W
W
D
6
W
W
D
4
W
W W
W
W
1
F
5
A
1
1
G/Y
On-Demand Gas Tankless Water Heater Service Manual
18

An “LC” or “00” error code indicates the unit is beginning to lime up and must be flushed. Failure to flush the
appliance will cause damage to the heat exchanger. Damage caused by lime build-up is not covered by the unit’s
warranty. After flushing, reset the LC fault code by turning off the power to the unit and turning the power back
on.
On-Demand
Gas Tankless
Water Heater
Pressure Relief Valve
3/4" Ball Valve
3/4" Union
Check Valve
S
Pressure Regulator
Circulating Pump
Solenoid Valve
Boiler Drain Valve
KEY
GasSupply
V1
V3
V2
V4
H1
H2
H3
Circulating Pump
5gallonpailof virgin,food
grade, white vinegar (or virgin,
food grade, citric acid).
Cold WaterLine
HotWaterLine
n-line
Filter
I
1. Disconnect electrical power to the water heater.
2. Close the shutoff valves on both the hot water and cold
water lines (V3 and V4).
3. Connect pump outlet hose (H1) to the cold water line at
service valve V2.
4. Connect drain hose (H3) to service valve V1.
5. Pour approximately 4 gallons of virgin, food grade, white
vinegar or citric acid into pail.
6. Place the drain hose (H3) and the hose (H2) to the pump
inlet into the cleaning solution.
7. Open both service valves (V1 and V2) on the hot water and
cold water lines.
8. Operate the pump and allow the cleaning solution to
circulate through the water heater for at least 45 minutes.
9. Turn off the pump.
10. Rinse the cleaning solution from the water heater as follows:
a. Remove the free end of the drain hose (H3) from the pail.
b. Close service valve, (V2), and open shutoff valve, (V4).
Do not open shutoff valve, (V3).
c. Allow water to flow through the water heater for 5 minutes
d. Close service valve, (V1), and open shutoff valve, (V3).
11. Disconnect all hoses.
12. With (V4) closed, remove the in-line
filter at the cold water inlet and clean
out any residue. Place filter back
into unit and open (V4).
13. Restore electrical power to the
water heater.
Flushing the Heat Exchanger
On-Demand Gas Tankless Water Heater Service Manual
19
IN-LINE CLEANING FILTER INSTRUCTIONS:

Component Replacement Instructions
Ignition line
Six screws
Wire harness connector
PC Board (dip switches)
Three screws
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Remove four screws securing the front panel. Remove front panel.
4. Pull out wire harness connector at the gas manifold assembly. See Figure 1.
5. Move aside the ignition line by pulling it out from the clear plastic tubing.
6. Remove the six screws that attach the gas manifold to the combustion chamber (part of the heat
exchanger assembly).
7. Remove the three screws that attach the gas manifold to the gas valve. Pull out the gas manifold.
Figure 1
8. Remove the four screws attaching the gas connection to the underneath side of the water heater.
See Figure 2.
Figure 2 Gas connection attached with 4 screws
Regulator screw access
9. Pull the gas connection down to disconnect it from the gas control assembly.
10. Pull out the gas control assembly. Remove the wire harness from the 4 solenoids.
11. Replace the O-ring (included in kit) where the assembly attaches to the gas connection. Make sure
the old O-ring is removed and discarded. Install the new gas control assembly.
WARNING Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
305e/o, 305i, 505e/o, 505i
On-Demand Gas Tankless Water Heater Service Manual
20
Gas Control Assembly