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.
On-Demand Gas Tankless Water Heater Service Manual
°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”
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
H
MODULATING
SOLENOID VALVE
FLAME ROD
MAIN SOLENOID VALVE
SOLENOID VALVE 1
SOLENOID VALVE 2
SOLENOID VALVE 3
POV
H
3
P
P
Y
4
H
5
P
SV0
BK
H
6
Y
SV1
BK
H
7
BL
SV2
BK
H
8
BR
SV3
BK
On-Demand Gas Tankless Water Heater Service Manual
G/Y
GND
SURGE
PROTECTOR
1
BL
3
BR
D
1
17
G/Y
GND
(CN3)
BL
BR
D
1
3
BLBL
(W) (W)
D
3
FROST SENSING
SWITCH
D
5
ANTI-FROST HEATER
W
W
D
2
BK
3
1
W
FUSE
(3A)
BKW
AC120VAC120V
HOT
HOT
NEUTRAL
NEUTRAL
D
BLBL
4
ANTI-FROST HEATER
GROUND
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
Y
ORW
BR
1
G
BY-PASS FLOW
CONTROL DEVICE
G
FREEZE PROTECTION
R
1
F
RR
2
F
(OPTIONAL)
On-Demand Gas Tankless Water Heater Service Manual
Y
Y
QS
WATER FLOW
13
O
O
2
H
R
6
RBKY
W
1
E
FM
F
R
BK
BK
W
W
P
W
Y
BLRBR
GY
4
3
F
F
W
W
W
W
R
BL
BRYGY
5
F
COMBUSTION FAN
WATER THERMISTOR
HEAT EXCHANGER
SENSOR
WATER THERMISTO R
OUTGOING WATER
ATER FLOW
CONTROL DEVICE
THERMAL FUSES
POV
W
1
H
W
RR
OVERHEAT
SWITCH
P
BK
4
3
H
H
SV0
SOLENOID VALVE
MODULATING
MAIN SOLENOID VALVE
R
SOLENOID VALVE 1
BK
SV1
O
Y
BK
SOLENOID VALVE 2
SV2
(LEFT)
BK
6
H
SV3
(RIGHT)
SOLENOID VALVE 3
5
H
(CENTER)
18
Flushing the Heat Exchanger
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.
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.
V1
On-Demand
Gas Tankless
Water Heater
n
I
lin
-
e
F
ilt
e
r
V2
G
a
s
S
u
p
p
y
l
IN-LINE CLEANING FILTER INSTRUCTIONS:
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.
5gallonpailof virgin,food
grade, white vinegar (or virgin,
food grade, citric acid).
KEY
3/4" Ball Valve
3/4" Union
Check Valve
Pressure Relief Valve
Pressure Regulator
Circulating Pump
Boiler Drain Valve
S
Solenoid Valve
H3
H
o
t
H2
Circulating Pump
V4
V3
C
o
ld
W
r
L
in
e
e
t
W
te
a
in
r
L
e
a
H1
On-Demand Gas Tankless Water Heater Service Manual
19
Component Replacement Instructions
305e/o, 305i, 505e/o, 505i
Gas Control Assembly
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.
Ignition line
Six screws
Wire harness connector
PC Board (dip switches)
Three screws
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
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.
WARNING
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
Regulator screw access
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.
On-Demand Gas Tankless Water Heater Service Manual
20
Component Replacement Instructions
Gas Control Assembly
305e/o, 305i, 505e/o, 505i
12. Attach wire harness to the 4 solenoids as s
SV0 black / pink
Figure 3
13. Install the gas manifold using 2 new packings (included in kit) between the manifold and the heat
exchanger. Replace the two circular gaskets (included in kit) in the gas valve (Figure 5).
Upper packing
Lower packing
(U shaped)
hown in Figure 3 below.
wolley / kcalb 1VS eulb / kcalb 2VS
POV pink / pink
(connector not shown)
Circular gaskets (re-use)
in gas valve
Figure 4
14. Start the three screws that attach the gas manifold to the gas valve. Tighten the six screws that hold
the gas manifold to the combustion chamber. Finish tightening the three screws that hold the gas
manifold to the gas valve.
15. Attach wiring harness connector (black & brown wires) to the gas manifold.
16. Attach ignition line.
17. Perform the Gas Pressure Setting Procedure.
Figure 5
On-Demand Gas Tankless Water Heater Service Manual
21
Component Replacement Instructions
705e/o (ASME),
705i (ASME)
Gas Control Assembly
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. On indoor models, remove the bracket holding
the controller (1 screw). (Figure 6)
5. Move aside the ignition line by pulling it out from
the clear plastic tubing. (Figure 6)
6. Remove the 5 screws that attach the gas
manifold to the combustion chamber (part of the
heat exchanger assembly). (Figure 7)
7. Remove the 2 screws that attach the gas
manifold to the gas valve. These screws are
machine screws and must be used at these
locations. (Figure 7)
8. Pull out the gas manifold and remove the
connector at the ignitor at the left side of the gas
manifold.
9. Remove the 3 screws attaching the gas
connection to the underneath side of the water
heater. (Figure 8)
Bracket screw
Figure 6
(indoor models)
5 screws
(gas manifold)
2 machine screws
(gas valve)
Remove the screw attaching the gas valve to the
10.
rear of the case.
11. Pull the gas connection down to disconnect it
from the gas control assembly.
Figure 7
Figure 8
Water line connections
Regulator
screw
access
Gas connection
attached with 3 screws
On-Demand Gas Tankless Water Heater Service Manual
22
Component Replacement Instructions
Gas Control Assembly
705e/o (ASME),
705i (ASME)
WARNING
12. Pull out the gas control assembly. Remove the
wire harness from the 2 solenoids.
13. Install the gas valve and attach the wire harness
to the 2 solenoids. (Figure 9)
14. Install the gas connection with 3 screws.
15. Replace the circular gasket (included in kit) in the
gas valve. (Figure 10)
16. Start the 2 screws that attach the gas manifold to
the gas valve. Tighten the 5 screws that hold the
gas manifold to the combustion chamber. Finish
tightening the 2 screws that hold the gas manifold
to the gas valve.
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
black / orange
orange / orange
Figure 9
Gasket
17. Attach ignition line.
18. On indoor models, install the bracket with the
controller.
19. Perform the Gas Pressure Setting Procedure.
On-Demand Gas Tankless Water Heater Service Manual
Figure 10
23
Component Replacement Instructions
305e/o, 505e/o
Fan
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply.
4. Remove four screws securing the front panel. Remove front panel.
5. Disconnect wire harness at the fan assembly. Disconnect the air temperature thermistor (two white
wires) at the connection with the white and orange wires within the wire bundle.
6. Pull out the harness attached to the solenoid on the manifold to make room to pull out the fan as-
sembly.
7. Remove the two screws that attach the fan assembly to the bottom of the burner.
Two screws
Figure 11
Solenoid on
the manifold
Wire harness connection
on the fan assembly
8. Pull out the fan assembly.
9. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with two screws.
10. Attach the wire harness to the solenoid on the gas manifold (brown,
11. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
12. Attach the air temperature thermistor (white, white wires) to the wire harness.
13. Install front panel using 4 screws.
14. Turn on water supply, power supply, and gas supply.
black wires).
On-Demand Gas Tankless Water Heater Service Manual
24
Component Replacement Instructions
305i, 505i
Fan
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply.
4. Remove four screws securing the front panel. Remove front panel.
5. Disconnect wire harness at the fan assembly. Disconnect the air temperature thermistor (two white
wires) at the connection with the white and orange wires within the wire bundle.
6. Pull out the harness attached to the solenoid on the manifold to make room to pull out the fan as-
sembly.
7. Loosen the ducting from the fan assembly by pinching open the metal clamp.
2 screws
Ducting and
metal clamp
Solenoid on the manifold
water flow servo
assembly
connection
Water outlet
connection
8. Remove the two screws that attach the fan assembly to the bottom of the burner.
9. Pull out the fan assembly.
10. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with two screws.
11. Push ducting over fan assembly inlet and secure with metal clamp.
12. Attach the wire harness to the solenoid on the gas manifold (brown, black wires).
Wire harness connection
on the fan assembly
Wire harness bundle
(air temperature
thermistor connection to
orange / white wires)
Figure 12
13. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
14. Attach the air temperature thermistor (white, white wires) to the wire harness.
15. Install front panel using 4 screws.
16. Turn on water supply, power supply, and gas supply.
On-Demand Gas Tankless Water Heater Service Manual
25
Fan
Component Replacement Instructions
705e/o (ASME),
705i (ASME)
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply.
4. Remove four screws securing the front panel.
Remove front panel.
5. On indoor models, remove the bracket holding
the controller (1 screw). (Figure 13)
6. Disconnect the wire harness at the fan
assembly. (Figure 14)
7. Remove the three screws attaching the fan
motor to the fan casing. (Figure 14)
8. Pull out the fan motor.
9. Install the new fan motor and tighten with three
screws.
10. Attach the wire harness to the fan assembly
(white, yellow, black, red wires).
11. On indoor models, install the bracket with the
remote controller.
12. Install front panel using 4 screws.
Bracket screw
Figure 13
(indoor m
odels)
13. Turn on water supply, power supply, and gas
supply.
Wire Harness Connector
Figure 14
3 screws
On-Demand Gas Tankless Water Heater Service Manual
26
Component Replacement Instructions
PC Board
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
305e/o, 305i, 505e/o, 505i
3. Turn off the water supply.
4. Remove four screws securing the front panel.
Remove front panel.
5. Remove the plastic guard covering the front of the
PC board.
6. Remove the controller connections.
7. If a surge protector with terminals is installed, then
remove this board by removing two screws. This
board should be re-installed on the replacement PC
board.
8. Remove the two screws at the top and bottom of the
PC board.
9. Pull out the PC board, remove plastic cover, and
remove the connections.
10. Adjust dip switches on the new PC board.
Switches 1-8 (SW1): Configure the dip switches the
same as on the original PC board. If necessary,
refer to the Dip Switch section or to the Operation
and Installation Manual for more information on
these dip switches.
Switches 1-6 (SW2): Replacement PC boards have
an additional bank of 6 dip switches. Configure
according to the diagrams on the following page
based on your model and gas type.
Figure 15
Screw
Remote controller
terminals
(NOT for 120 V power)
If these 2 terminals are
present then this is a
surge protector board
with terminals to
connect freeze
protection solenoid
valves and should be
installed with the new
PC board.
Attached with 2 screws
Screw
11. Attach connections and plastic cover.
12. Insert PC board and attach with two screws.
13. If a surge protector with terminals was installed on
the original PC board, remove it
new PC board. See Figure 15.
14. Attach connections for the remote controller.
15. Attach plastic guard.
16. Perform the Gas Pressure Setting Procedure.
On-Demand Gas Tankless Water Heater Service Manuals
and install it on the
27
PC Board
Component Replacement Instructions
305i, 305e, 505i, 505e
100/101 and 200/201 Series
SW2 setup for 505i
Propane (LPG) Natural Gas (NG)
Switch No.
ON
O
F
F
1
2
3
4
5
6
Switch No.
ON
O
F
F
1
2
3
4
5
6
SW2 setup for 305i
Propane (LPG) Natural Gas (NG)
Switch No.
ON
O
F
F
1
2
3
4
5
6
Switch No.
ON
O
F
F
1
2
3
4
5
6
SW2 setup for 505e
Propane (LPG) Natural Gas (NG)
Switch No.
ON
O
F
F
1
2
3
4
5
6
Switch No.
ON
O
F
F
1
2
3
4
5
6
SW2 setup for 305e
Propane (LPG) Natural Gas (NG)
Switch No.
ON
O
F
F
1
2
3
4
5
6
Switch No.
ON
O
F
F
1
2
3
4
5
6
On-Demand Gas Tankless Water Heater Service Manual
28
Component Replacement Instructions
705e/o (ASME), 705i (ASME)
PC Board
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. Remove the surge protector (2 screws)
5. Remove the 2 screws connecting the PC
board to the water heater casing.
6. Pull out the PC board and remove the
connections.
7. Adjust dip switches on the new PC board.
Figure 16
Screw
Burner test point
Potentiometer
SW1
SW2
Switches 1-8 (SW1):
Configure the dip switches the same as on the
original PC board. If necessary, refer to the
Dip Switch section or to the Operation and
Installation Manual for more information on
these dip switches.
Switches 1-4 (SW2) or Switches 1-6 (SW2):
Configure according to the diagrams based on
your model and gas type.
8. Attach connections and insert PC board.
Attach with 2 screws.
9. Attach the surge protector
with 2 screws.
10. Perform the Gas Pressure
Setting Procedure.
Propane (LPG) Natural Gas (NG)
Switch No.
O
F
F
SW2 setup for 705i
Switch No.
ON
1
2
3
4
5
6
O
F
F
ON
Screw
Surge
protector
Screw
SW2 setup for 705e/o
Propane (LPG) Natural Gas (NG)
Switch No.
ON
1
2
3
4
5
6
O
F
F
1
2
3
4
5
6
Switch No.
ON
O
F
F
1
2
3
4
5
6
On-Demand Gas Tankless Water Heater Service Manual
29
Component Replacement Instructions
Water Flow Control Assembly
305e/o, 305i, 505e/o, 505i
100/101 and 200/201 Series
NOTICE
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water from the appliance.
4. Remove four screws securing the front panel. Remove front panel.
Due to design changes, the new valve may appear different than the installed valve in
color, size, and in the number of wires in the harness connections.
Remove the water flow assembly
5. Remove 1 screw and bracket at the water flow assembly. The bracket can be left on the water line.
Pull out the water line. (Figure 17)
Figure 17
1 screw and bracket
(water flow assembly)
6. Remove the 4 screws attaching the water inlet to the underneath side of the water heater.
(Figure 18).
Figure 18
Water inlet
On-Demand Gas Tankless Water Heater Service Manual
30
Component Replacement Instructions
305e, 305i, 505e, 505i
100/101 and 200/201 Series
Water Flow Control Assembly
7. Pull out the water flow servo assembly and disconnect the cable harnesses. (Figure 19)
A.water flow sensor harness (black/yellow/red wires)
B.water flow servo harness (red/blue/brown/yellow/gray or red/blue/brown/orange/yellow/gray wires)
C.heating element
water flow servo connector
Figure 19
heating element
connector
water flow sensor
connector
Assemble
8. Place the new water flow assembly inside the water heater and attach the cable harnesses.
9. Replace the O-ring on the water inlet (included in kit). Attach the water flow assembly through the
bottom of the compartment to the water inlet using 4 screws. The 2 shorter screws can be installed
first to connect the water flow assembly to the bottom of the compartment. Then install the 2 longer
screws through the water inlet.
10. Replace the O-ring on the water line (included in kit). Attach the water line to the
assembly with 1 screw and bracket.
11. Install the front panel using 4 screws.
12. Turn on the water supply, power supply, and gas supply.
13. Open a hot water tap and ensure there are no leaks at the water heater.
water flow
On-Demand Gas Tankless Water Heater Service Manual
31
Component Replacement Instructions
100/101 and 200/201 Series
505e/o, 505i
Water Flow Control Assembly
NOTICE
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water from the appliance.
4. Remove four screws securing the front panel. Remove front panel.
Remove Fan Assembly (Figure 20)
5. Disconnect wire harness at the fan assembly. Disconnect the air temperature thermistor (two white wires) at
the connection with the white and orange wires within the wire bundle.
6. Pull out the harness attached to the solenoid on the manifold to make room to pull out the fan assembly.
7. Remove the 2 screws that attach the fan assembly to the bottom of the burner.
8. On indoor models, loosen the ducting from the fan assembly by pinching open the metal clamp.
9. Pull out the fan assembly.
Due to design changes, the new valve may appear different than the installed valve in
color, size, and in the number of wires in the harness connections.
Figure 20
2 screws
Ducting and
metal clamp
(indoor models
only)
Remove the water flow assembly (Figure 21)
10. Remove 2 screws and 2 brackets at the
flow servo assembly. The brackets can be
left on the water lines. Pull out the water
lines.
Water flow
servo assembly
connections
water
Solenoid on the manifold
Wire harness connection
on the fan assembly
Wire harness bundle
(connection to orange /
white wires)
Figure 21
On-Demand Gas Tankless Water Heater Service Manual
32
Component Replacement Instructions
505e, 505i
100/101 and 200/201 Series
Water Flow Control Assembly
11. Remove the 4 screws attaching the water inlet to the
underneath side of the water heater.
12. Disconnect the cable harnesses (Figure 23):
a. water flow sensor harness (black/yellow/red wires)
b. bypass servo assembly harness (white/red/yellow/orange/brown wires)
c. water flow servo harness (red/blue/brown/yellow/gray or red/blue/brown/orange/yellow/gray wires)
d. heating element
Figure 23
Figure 22
Water inlet
water flow servo
connector
water flow sensor
connector
13. Pull out the water flow servo assembly and bypass servo assembly.
14. Remove 2 screws in order to separate the bypass servo assembly
from the water flow servo assembly. (Figure 24)
Assemble
15. Replace the O-ring (included in kit) between the water flow servo assembly and the bypass servo assembly.
Attach the new water flow servo assembly to the bypass servo assembly with 2 screws.
16. Place in
17. Replace the O-ring on the water inlet (included in kit). Attach the water flow assembly to the water inlet using
4 screws. The 2 shorter screws can be installed first to connect the water flow assembly to the bottom of the
compartment. Then install the 2 longer screws through the water inlet.
18. Replace the O-ring on the water lines (included in kit). Attach the two water lines to the bypass servo
assembly with 1 screw each.
side the water heater and attach the cable harnesses.
water flow servo
connector
heating element
connector
Figure 24
19. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with two screws.
20. On indoor models, push the ducting over the fan assembly inlet and secure with the metal pinch clamp.
21. Attach the wire harness to
22. Install the front panel using 4 screws.
23. Turn on the water supply, power supply, and gas supply.
24. Open a hot water tap and ensure there are no leaks at the water heater.
the fan assembly (white, yellow, black, red wires).
On-Demand Gas Tankless Water Heater Service Manual
33
Component Replacement Instructions
Water Flow Control Assembly
1. Turn off the gas supply.
705e/o (ASME), 705i (ASME)
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water from the
appliance.
4. Remove four screws securing the front panel. Remove
front panel.
5. Remove 2 screws and 2 brackets at the water flow
servo assembly. Pull out the water lines. (Figure 25)
6. Remove the water flow sensor and the heating
element. (Figure 25)
7. Remove the 4 screws attaching the water inlet to the
underneath side of the water heater. (Figure 26)
8. Pull out the water flow servo assembly and bypass
servo assembly. Remove the wire harness from the
water servo valve. (Figure 27)
9. Remove 2 screws in order to separate the bypass
servo assembly from the water flow servo assembly.
(Figure 27)
10. Replace the O-ring (included in kit) be
flow servo assembly and the bypass servo assembly.
Attach the new water flow servo assembly to the
bypass servo assembly with 2 screws.
11. Attach the wire harness to the water servo valve.
tween the water
Figure 25
Figure 26
Water flow
sensor
Water
lines
Heating
element
Water
inlet
12. Place inside the water heater.
13. Attach the water flow assembly to the water inlet using
4 screws. The 2 shorter screws can be installed first to
connect the water flow assembly to the bottom of the
compartment. Install the 2 longer screws through the
water inlet.
14. Insert the heating element and attach the water flow
sensor.
15. Replace the O-ring on the water lines (included in kit).
Attach the two water lines to the bypass servo
assembly with 1 screw each.
16. Install the front panel using 4 screws.
17. Turn on the water supply, power su
supply.
18. Open a hot water tap and ensure there are no leaks at
the water heater.
pply, and gas
On-Demand Gas Tankless Water Heater Service Manual
34
Bypass
servo
Wire harness
Screws (2)
Water flow
servo
Figure 27
Component Replacement Instructions
Heat Exchanger
1. Turn off the gas supply.
305e
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front panel.
Remove front panel.
Remove Fan Assembly (Figure 29)
5. Disconnect wire harness at the fan assembly.
Disconnect the air temperature thermistor
(two white wires) at the connection with the
white and orange wires within the wire
bundle.
6. Pull out the harness attached to the solenoid
on the manifold to make room to pull out the
fan assembly.
7. Remove the 2 screws that attach the fan
assembly to the bottom of the burner.
8. Pull out the fan assembly.
Figure 28
Figure 29
2 screws
Burner cover
plate
Gas Manifold
PC Board
Gas Control
Valve
Fan Assembly
Solenoid
Wire
harness
connection
Disconnect Water Lines (Figure 30)
9. Remove 1 screw from the water outlet
bracket. Remove the bracket by rotating and
moving it up toward the bend in the tube
where the diameter is smaller.
10. Remove 1 screw and 1 b
flow servo assembly.
racket at the water
On-Demand Gas Tankless Water Heater Service Manual
Figure 30
35
Water outlet
connection
Water flow servo
assembly connection
Component Replacement Instructions
Heat Exchanger
305e
Disconnect PC Board (Figure 31)
11. Remove 1 screw connecting the PC
Board to the heat exchanger assembly.
Remove Gas Manifold (Figure 31)
12. Remove the 6 screws that attach the gas
manifold to the combustion chamber
(part of the heat exchanger assembly).
13. Remove the 3 screws that attach the gas
manifold to the gas valve. These screws
are machine screws and must be used at
these locations.
14. Pull out the ignition line and remove the
gas manifold.
Figure 31
Remove Burner and Burner Cover Plate (Figure 32)
15. Remove the 8 screws attaching the burner cover plate to the combustion chamber. Move the cover plate to
the side. It is not necessary to disconnect the wire harness from the burner cover plate.
16. Remove the 2 screws attaching the burner to the heat exchanger. Pull out the burner.
Ignition line
6 screws (gas manifold)
PC Board screw
3 machine screws
(gas valve)
17. Unscrew the ignition line connection. (Figure 32)
8 screws
(burner cover plate)
2 screws (burner)
Figure 32
Ignition line
connection
Disconnect Wire Harness Attachments and Screws Holding the Heat Exchanger
18. Remove the wire harness
small O-ring in the thermistor is removed.
19. Remove 3 screws behind the fan. (Figure 33)
20. Remove 2 screws above the exhaust. Pull assembly from the unit. (Figure 34)
attachments - sensors, heating elements, fusible link brackets. Ensure that the
Figure 33
Figure 34
3 screws
On-Demand Gas Tankless Water Heater Service Manual
2 screws
36
Component Replacement Instructions
Heat Exchanger
WARNING
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
305e
Installation
21. Install the largest O-ring (included in kit) over the water outlet tube and the two smaller O-rings (included in kit)
over the bypass servo tubes. (Figure 30)
22. Remove any other attached items and install on the new heat exchanger.
23. Install the new heat exchanger using 2 screws above the exhaust and 3 screws behind the fan. (Figures 33, 34)
Connect Pressure Tube and Wire Harness Attachments
24. Connect wire harness attachments.
25. Connect the pressure tube.
26. Attach the ignition line connection with 1 screw.
Install Burner and Burner Cover Plate (Figure 32)
27. Replace the combustion chamber packing (included in kit) removing any residue from old packing. Insert the
burner and place the burner cover plate into position. Attach the burner cover plate first with 8 screws and
attach the burner with 2 screws.
then
Install Gas Manifold and Connect PC Board
28. Make sure that the two black packings (Figure 35) are intact on the gas control
assembly. Attach the gas manifold with 3 machine screws at the gas control
assembly. Replace the lower and upper packings (included in kit) for the
manifold plate removing any residue.
29. Attach the gas manifold with 6 screws at heat exchanger.
30. Attach the ignition line at the burner cover plate.
31. Attach the PC Board to the heat exchanger with 1 screw.
Figure 35
Connect Water Lines (Figure 30)
32. Attach the water outlet line and bracket with 1 screw.
33. Attach the line to the water flow servo assembly with 1 screw and 1 bracket.
Install Fan Assembly (Figure 29)
34. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with
35. Attach the wire harness to the solenoid on the gas manifold (brown, black wires).
36. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
37. Attach the air temperature thermistor (white, white wires) to the wire harness.
38. Install the front panel using 4 screws.
two screws.
39. Turn on the water supply, power supply, and gas supply.
40. Check for gas leaks.
On-Demand Gas Tankless Water Heater Service Manual
37
Component Replacement Instructions
505e/o
Figure 36
Heat Exchanger
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front panel.
Remove front panel.
Remove Fan Assembly (Figure 37)
5. Disconnect wire harness at the fan assembly.
Disconnect the air temperature thermistor
(two white wires) at the connection with the
white and orange wires within the wire
bundle.
Figure 37
2 screws
Burner cover
plate
Gas Manifold
PC Board
Gas Control
Valve
Fan Assembly
Solenoid
6. Pull out the harness attached to the solenoid
on the manifold to make room to pull out the
fan assembly.
7. Remove the 2 screws that attach the fan
assembly to the bottom of the burner.
8. Pull out the fan assembly.
Disconnect Water Lines (Figure 38)
9. Remove 1 screw from the water outlet
bracket. Remove the bracket by rotating and
moving it up toward the bend in the tube
where the diameter is smaller.
10. Remove 2 screws and 2
bypass servo assembly.
brackets at the
Figure 38
Water outlet
connection
Wire
harness
connection
Bypass servo assembly
connections
On-Demand Gas Tankless Water Heater Service Manual
38
Component Replacement Instructions
505e/o
Heat Exchanger
Disconnect PC Board (Figure 39)
11. Remove 1 screw connecting the PC
Board to the heat exchanger
assembly.
Remove Gas Manifold (Figure 39)
12. Remove the 6 screws that attach the
gas manifold to the combustion
chamber (part of the heat exchanger
assembly).
13. Remove the 3 screws that attach the
gas manifold to the gas valve. These
screws are machine screws and must
be used at these locations.
Ignition line
6 screws (gas manifold)
PC Board screw
3 machine screws
(gas valve)
Remove Burner and Burner Cover Plate (Figure 40)
14. Pull out the ignition line and remove the gas manifold.
15. Remove the 8 screws attaching the burner cover plate to the combustion chamber. Move the cover
plate to the side. It is not necessary to disconnect the wire harness from the burner cover plate.
Figure 39
16. Remove the 2 screws attaching the burner to the heat exchanger. Pull out the burner.
8 screws
(burner cover plate)
2 screws (burner)
Figure 40
Ignition line
connection
Disconnect Wire Harness Attachments and Screws Holding the Heat Exchanger
17. Unscrew the ignition line connection. (Figure 40)
18. Remove the wire harness attachments - sensors,
that the small O-ring in the thermistor is removed.
19. Remove 3 screws behind the fan. (Figure 41)
Figure 41
heating elements, fusible link brackets. Ensure
Figure 42
3 screws
On-Demand Gas Tankless Water Heater Service Manual
2 screws
39
Heat Exchanger
Component Replacement Instructions
505e/o
WARNING
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
Installation
20. Remove 2 screws above the exhaust. Pull assembly from the unit. (Figure 42)
21. Install the largest O-ring (included in kit) over the water outlet tube and the two smaller O-rings
(included in kit) over the bypass servo tubes. (Figure 38)
22. Remove any other attached items and install on the new heat exchanger.
Connect Pressure Tube and Wire Harness Attachments
23. Install the new heat exchanger using 2 screws above the exhaust and 3 screws behind the fan.
(Figures 41, 42)
Install Burner and Burner Cover Plate (Figure 40)
24. Connect wire harness attachments.
25. Connect the pressure tube. Attach the ignition line connection with 1 screw.
Install Gas Manifold and Connect PC Board
26. Replace the combustion chamber packing (included in kit) removing
any residue from old packing. Insert the burner and place the burner
cover p
screws and then attach the burner with 2 screws.
late into position. Attach the burner cover plate first with 8
27. Make sure that the two black packings (Figure 43) are intact on the
gas control assembly. Attach the gas manifold with 3 machine screws
at the gas control assembly. Replace the lower and upper packings
(included in kit) for the manifold plate removing any residue.
Figure 43
Connect Water Lines (Figure 38)
28. Attach the gas manifold with 6 screws at heat exchanger.
29. Attach the ignition line at the burner cover plate.
Install Fan Assembly (Figure 37)
30. Attach the PC Board to the heat exchanger with 1 screw.
31. Attach the water outlet line and bracket with 1 screw.
32. Attach the two lines to the bypass servo assembly with 1 screw and 1 bracket for each line.
33. Install the fan assembly by inserting the tab on the fan assembly int
exchanger and attaching with two screws.
34. Attach the wire harness to the solenoid on the gas manifold (brown, black wires).
35. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
o the slot at the base of the heat
On-Demand Gas Tankless Water Heater Service Manual
40
Component Replacement Instructions
Heat Exchanger
1. Turn off the gas supply.
305i
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front panel.
Remove front panel.
Figure 44
Burner cover
plate
Remove Fan Assembly (Figure 45)
5. Disconnect wire harness at the fan assembly.
Disconnect the air temperature thermistor
(two white wires) at the connection with the
white and orange wires within the wire
bundle.
6. Pull out the harness attached to the solenoid
on the manifold to make room to pull out the
fan assembly.
7. Remove the 2 screws that attach the fan
assembly to the bottom of the burner.
8. Loosen the ducting
pinching open the metal clamp.
9. Pull out the fan assembly.
from the fan assembly by
Gas Manifold
PC Board
Gas Control
Valve
Fan Assembly
Disconnect Water Lines and PC Board (Figure 45)
10. Remove 1 screw from the water outlet bracket. Remove the bracket by rotating and moving it up
toward the bend in the tube where the diameter is smaller.
11. Remove the screw and bracket at the water flow servo assembly.
12. Remove 1 screw connecting the PC Board to the heat exchanger assembly.
2 screws
Ducting and
metal clamp
Solenoid on the manifold
water flow servo
assembly
connection
Water outlet
connection
Wire harness connection
on the fan assembly
Wire harness bundle
(air temperature
thermistor connection to
orange / white wires)
On-Demand Gas Tankless Water Heater Service Manual
41
Figure 45
PC board screw
Component Replacement Instructions
Heat Exchanger
305i
Remove Gas Manifold (Figure 46)
13. Remove the 6 screws that attach the gas manifold to the combustion chamber (part of the heat exchanger
assembly).
14. Remove the 3 screws that attach the gas manifold to the gas valve. These screws are machine screws and
must be used at these locations.
15. Pull out the ignition line and remove the gas manifold.
Figure 46
Ignition line
6 screws (gas manifold)
PC Board screw
3 machine screws
(gas valve)
Remove Burner and Burner Cover Plate (Figure 47)
16. Remove the 8 screws attaching the burner cover plate to the combustion chamber. Move the cover plate to
the side. It is not necessary to disconnect the wire harness from the burner cover plate.
17. Remove the 2 screws attaching the burner to the heat exchanger. Pull out the burner.
18. Disconnect the pressure tube from the heat exchanger and unscrew the ignition line connection.
Figure 47
8 screws
(burner cover plate)
Pressure tube
2 screws (burner)
Ignition line
connection
On-Demand Gas Tankless Water Heater Service Manual
42
Component Replacement Instructions
305i
Heat Exchanger
Disconnect Wire Harness Attachments
19. Remove the wire harness attachments - sensors, heating elements, fusible link brackets. Ensure
that the small O-ring in the thermistor is removed.
Remove Heat Exchanger and Air Intake/Exhaust
20. Remove 8 screws connecting the assembly to the water heater casing assembly. (Figures 48, 49)
Figure 48
1 screw
Near fan assembly location
3 screws
At right and left upper corners of water heater
2 screws 2 screws
Figure 49
Separate the Heat Exchanger from the Air Intake/Exhaust
21. Pull out the assembly. Remove 3 brackets on the side and back holding the fusible link.
22. Remove the 9 screws at the cover plate over the air intake passage. (Figure 50)
23. Remove the 4 screws attaching the heat exchanger to the air intake/exhaust assembly. (Figure 51)
Figure 50
9 screws
(cover plate)
Figure 51
4 screws
24. Pull apart the heat exchanger and air intake/exhaust assembly. (Figure 52)
25. Remove 4 screws attaching the bracket on top of the heat exchanger. Pull off the bracket. (Figure 53)
Figure 52
WARNING
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
On-Demand Gas Tankless Water Heater Service Manual
4 screws
(bracket)
Figure 53
43
Component Replacement Instructions
305i
Heat Exchanger
Install Packings and Bracket
26. Install the O-ring (included in kit) over the water outlet tube and the O-ring (included in kit) over the water flow
servo tube. (Figure 45)
27. Install the bracket over the replacement heat exchanger. Push evenly on both sides of the bracket. Attach
with four screws. (Figure 54)
Combine the Heat Exchanger and the Air Intake/Exhaust Assembly
28. Push the heat exchanger into the air intake/exhaust assembly. Attach with four screws. (Figure 51)
29. Attach the cover plate over the air intake passage with 9 screws. (Figure 51)
Install Heat Exchanger and Air Intake/Exhaust Assembly (Figures 48, 49)
30. Attach the fusible link to the back (2 brackets) and side (1 bracket). Slide the assembly into the casing
assembly and attach with 8 screws starting at the top of the water heater.
Connect Pressure Tube and Wire Harness Attachments
31. Connect wire harness attachments.
32. Connect the pressure tube. Attach the ignition line connection with 1 screw. (Figure 47)
Install Burner and Burner Cover Plate (Figure 47)
33. Replace the combustion chamber packing (included in kit) removing any residue from old packing. Insert the
burner and place the burner cover plate into position. Attach the burner cover plate first with 8 screws and
then attach the burner with 2 screws.
Install Gas Manifold and Connect PC Board
34. Make sure that the two black packings (Figure 54) are intact on the
gas control assembly. Attach the gas manifold with 3 machine
screws at the gas control assembly. Replace the lower and upper
packings (included in kit) for the manifold plate removing any residue.
35. Attach the gas manifold with 6 screws at heat exchanger.
36. Attach the ignition line at the burner cov
er plate.
Connect Water Lines (Figure 45)
37. Attach the PC Board to the heat exchanger with 1 screw.
38. Attach the water outlet line and bracket with 1 screw.
39. Attach the two lines to the bypass servo assembly with 1 screw and 1 bracket for each line.
Figure 54
Install Fan Assembly (Figure 45)
40. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with two screws.
41. Push the ducting over the fan assembly exit and secure with the metal pinch clamp.
42. Attach the wire harness to the solenoid on the gas manifold (brown, black wires).
43. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
44. Attach the air temperature thermistor (white, white wires) to the wire harness.
45. Install the front panel using 4
46. Turn on the water supply, power supply, and gas supply.
47. Check for gas leaks.
screws.
On-Demand Gas Tankless Water Heater Service Manual
44
Component Replacement Instructions
Heat Exchanger
505i
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front panel.
Remove front panel.
Remove Fan Assembly (Figure 56)
5. Disconnect wire harness at the fan assembly.
Disconnect the air temperature thermistor
(two white wires) at the connection with the
white and orange wires within the wire
bundle.
6. Pull out the harness attached to the solenoid
on the manifold to make room to pull out the
fan assembly.
7. Remove the 2 screws that attach the fan
assembly to the bottom of the burner.
Figure 55
Burner cover
plate
Gas Manifold
PC Board
Gas Control
Valve
Fan Assembly
8. Loosen the ducting from the fan assembly by
pinching open the metal clamp.
9. Pull out the fan assembly.
2 screws
Ducting and
metal clamp
Figure 56
Solenoid on the manifold
Wire harness connection
on the fan assembly
Wire harness bundle
(air temperature
thermistor connection to
orange / white wires)
On-Demand Gas Tankless Water Heater Service Manual
45
Component Replacement Instructions
Heat Exchanger
505i
Disconnect Water Lines (Figure 57)
10. Remove 1 screw from the water outlet bracket. Remove the bracket by rotating and moving it up
toward the bend in the tube where the diameter is smaller.
11. Remove 2 screws and 2 brackets at the bypass servo assembly.
Figure 57
Water outlet
connection
Disconnect PC Board (Figure 58)
12. Remove 1 screw connecting the PC Board to the heat exchanger assembly.
Bypass servo
assembly
connections
Remove Gas Manifold (Figure 58)
13. Remove the 6 screws that attach the gas manifold to the combustion chamber (part of the heat
exchanger assembly).
14. Remove the 3 screws that attach the gas manifold to the gas valve. These screws are machine
screws and must be used at these locations.
15. Pull out the ignition line and remove the gas manifold.
Figure 58
Ignition line
6 screws (gas manifold)
PC Board
3 machine screws
(gas valve)
screw
On-Demand Gas Tankless Water Heater Service Manual
46
Component Replacement Instructions
505i
Heat Exchanger
Remove Burner and Burner Cover Plate (Figure 59)
16. Remove the 8 screws attaching the burner cover plate to the combustion chamber. Move the cover
plate to the side. It is not necessary to disconnect the wire harness from the burner cover plate.
17. Remove the 2 screws attaching the burner to the heat exchanger. Pull out the burner.
Figure 59
8 screws
(burner cover plate)
Pressure tube
2 screws (burner)
Ignition line
connection
Disconnect Gas Line and Wire Harness Attachments
18. Disconnect the pressure tube from the heat exchanger and unscrew the ignition line connection.
(Figure 59)
19. Remove the wire harness attachments - sensors, heating elements, fusible link brackets. Ensure
that the small O-ring in the thermistor is removed. (Figure 60)
Sensors
Heating
elements
Figure 60
Thermistor
Brackets for
fusible link
On-Demand Gas Tankless Water Heater Service Manual
47
Component Replacement Instructions
Heat Exchanger
505i
Remove Heat Exchanger and Air Intake/Exhaust
20. Remove 8 screws connecting the assembly to the water heater casing assembly. (Figures 61, 62)
At right and left upper corners of water heater Near fan assembly location
Figure 61
1 screw
3 screws
2 screws 2 screws
Figure 62
Separate the Heat Exchanger from the Air Intake/Exhaust
21. Pull out the assembly. Remove 3 brackets on the side and back holding the fusible link.
22. Remove the 9 screws at the cover plate over the air intake passage. (Figure 63)
23. Remove the 4 screws attaching the heat exchanger to the air intake/exhaust assembly. (Figure 64)
Figure 63
Figure 64
9 screws
(cover plate)
4 screws
24. Pull apart the heat exchanger and air intake/exhaust assembly. (Figure 65)
25. Remove 4 screws attaching the bracket on top of the heat exchanger. Pull off the bracket. (Figure 66)
4 screws
(bracket)
Figure 66
Figure 65
WARNING
Failure to correctly assemble the components according to these instructions
could result in a gas leak or explosion.
Install Packings and Bracket
26. Install the largest O-ring (included in kit) over the water outlet tube and the two smaller O-rings (included in kit)
over the bypass servo tubes. (Figure 57)
27. Install the bracket over the replacement heat exchanger. Push evenly on both sides of the bracket. Attach
with four screws. (Figure 66)
On-Demand Gas Tankless Water Heater Service Manual
48
Component Replacement Instructions
505i
Heat Exchanger
Combine the Heat Exchanger and the Air Intake/Exhaust
28. Push the heat exchanger into the air intake/exhaust assembly. Attach with four screws. (Figure 64)
29. Attach the cover plate over the air intake passage with 9 screws. (Figure 63)
Install Heat Exchanger and Air Intake/Exhaust Assembly (Figures 61, 62)
30. Attach the fusible link to the back (2 brackets) and side (1 bracket). Slide the assembly into the
casing assembly and attach with 8 screws starting at the top of the water heater.
Connect Pressure Tube and Wire Harness Attachments
31. Connect wire harness attachments. (Figure 60)
32. Connect the pressure tube.
33. Attach the ignition line connection with 1 screw. (Figure 59)
Install Burner and Burner Cover Plate (Figure 59)
34. Replace the combustion chamber packing (included in kit) removing any residue from old packing. Insert the
burner and place the bur
then attach the burner with 2 screws.
ner cover plate into position. Attach the burner cover plate first with 8 screws and
Install Gas Manifold and Connect PC Board
35. Make sure that the two black packings (Figure 67) are intact on the
gas control assembly. Attach the gas manifold with 3 machine
screws at the gas control assembly. Replace the lower and upper
packings (included in kit) for the manifold plate removing any residue.
36. Attach the gas manifold with 6 screws at heat exchanger.
37. Attach the ignition line at the burner cover plate.
Connect Water Lines (Figure 57)
38. Attach the PC Board to the heat exchanger with 1 screw.
39. Attach the water outlet line and bracket with 1 screw.
40. Attach the two lines to the bypass servo assembly with 1 screw and 1 bracket for each line.
Figure 67
Install Fan Assembly (Figure 56)
41. Install the fan assembly by inserting the tab on the fan assembly into the slot at the base of the heat
exchanger and attaching with two screws.
42. Push the ducting over the fan assembly exit and secure with the metal pinch clamp.
43. Attach the wire harness to the solenoid on the gas manifold (brown, black wires).
44. Attach the wire harness to the fan assembly (white, yellow, black, red wires).
45. Attach the air temperature thermistor (white, white wires) to the wire harness.
46. Install the front panel using 4 screws.
47. Turn on the water supply, power supply, and gas supply.
48. Check for gas leaks.
On-Demand Gas Tankless Water Heater Service Manual
49
Component Replacement Instructions
705e/o (ASME)
Heat Exchanger
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front
panel. Remove front panel.
5. Disconnect wire harness at the fan
assembly, the electrical connections to
the 3 solenoid valves, and the ignition
line.
6. Remove 3 screws and brackets securing
the water line connections. (Figure 68)
7. Remove the 5 screws that attach the gas
manifold to the combustion chamber
(part of the heat exchanger assembly).
(Figure 68)
8. Remove the 2 screws that attach the gas
manifold to the gas valve. These screws
are machine screws and must be used at
these locations. (Figure 68)
5 screws
(gas manifold)
Figure 68
2 machine screws
(gas valve)
Water line connections
9. Pull out the gas manifold and remove the
connector at the ignitor at the left side of
the gas manifold.
10. Remove
burner cover plate to the combustion
chamber. (Figure 69)
11. Remove the 2 screws attaching the
burner to the heat exchanger. Pull out
the burner. (Figure 69)
12. Remove the wire harness attachments sensors, heating elements, fusible link
brackets. Ensure that the small O-ring at
the thermistor is removed.
13. Remove the 4 screws connecting the
heat exchanger to the casing. (Figure 70)
14. Pull out the assembly. Remove the
brackets on the side and back holding
the fusible link. Slide off the fusible link.
the 9 screws attaching the
Figure 69
9 screws
(burner cover plate)
Top screws
2 screws
(burner)
On-Demand Gas Tankless Water Heater Service Manual
Figure 70
50
Bottom screws
Component Replacement Instructions
Heat Exchanger
705e/o (ASME)
15. Remove the fan assembly (4 screws) and
install it on the new heat exchanger. (Figure 71)
16. Remove the flue outlet (6 screws) and install it
on the new heat exchanger. (Figure 72)
17. Install the largest O-ring (included in kit) over
the water outlet tube and the two smaller Orings (included in kit) over the water inlet
tubes. (Figure 71)
18. Slide the fusible link between the water outlet
and inlet tubes and onto the new heat
exchanger. (Figure 71)
19. Attach brackets at the back and side holding
the fusible link.
20. Install the 4 screws at the top and bottom of
the heat exchanger to the casing. (Figure 70)
21. Insert the burner and place the burner cover
plate into position. Attach the burner cover
plate first with 9 screws and then attach the
burner with 2 screws. (Figure 69)
22. Replace
23. Make sure that the black gasket (Figure 74) is
intact on the gas control assembly. Replace
the lower and upper gaskets (included in kit)
for the manifold plate removing any residue.
(Figure 75)
the electrode gasket. (Figure 73)
Figure 72
Figure 73
4 locations
Figure 71
Water
outlet tube
Water inlet
tubes
Electrode
Gasket
24. Attach the electrical connector to the ignitor
on the manifold and attach the gas manifold
with 2 machine screws at the gas control
assembly. (Figure 68)
25. Attach the gas manifold with 5 screws at heat
exchanger. (Figure 68)
26. Connect wire harness attachments.
27. Attach the ignition line at the burner cover
plate.
28. Attach the 3 electrical connectors to the
solenoid valves.
29. Attach the wire harness to the fan assembly
(white, yellow, black, red wires).
30. Attach the brackets to the water line
connections. (Figure 68)
31. Install the front panel using 4 screws. Turn
the water supply, power supply, and gas
supply. Check for gas leaks.
on
On-Demand Gas Tankless Water Heater Service Manual
Gasket
Figure 74
Figure 75
Gaskets
51
Component Replacement Instructions
Heat Exchanger
1. Turn off the gas supply.
2. Turn off the 120 V power supply.
3. Turn off the water supply. Drain all water
from the appliance.
4. Remove four screws securing the front
panel. Remove front panel.
5. Remove the bracket holding the
controller (1 screw). (Figure 76)
6. Disconnect wire harness at the fan
assembly, the electrical connections to
the 3 solenoid valves, and the ignition
line.
7. Remove 3 screws and brackets securing
the water line connections. (Figure 77)
8. Remove the 5 screws that attach the gas
manifold to the combustion chamber
(part of the heat exchanger assembly).
(Figure 77)
9. Remove the 2 screws that attach the gas
manifold to the gas valve. These screws
are machine screws and must be used at
these locations. (Figure 77)
705i (ASME)
Bracket screw
Figure 76
5 screws
(gas manifold)
2 machine screws
(gas valve)
10. Pull out the gas manifold and re
connector at the ignitor at the left side of
the gas manifold.
11. Remove the 9 screws attaching the
burner cover plate to the combustion
chamber. (Figure 78)
12. Remove the 2 screws attaching the
burner to the heat exchanger. Pull out
the burner. (Figure 78)
13. Remove the wire harness attachments -
sensors, heating elements, fusible link
brackets. Ensure that the small O-ring at
the thermistor is removed.
move the
Figure 77
Figure 78
Water line connections
9 screws
(burner cover plate)
2 screws
(burner)
On-Demand Gas Tankless Water Heater Service Manual
52
Component Replacement Instructions
Heat Exchanger
14. Remove the 3 screws at the seal plate at
the top of the water heater. Remove the
seal plate and gasket. (Figure 79)
15. Remove flue outlet vent (4 screws).
(Figure 80)
16. Remove the 4 screws connecting the
heat exchanger to the back of the casing.
(Figure 81)
17. Pull out the assembly. (It is hooked on
brackets in the casing.) Remove the
brackets on the side and back holding
the fusible link. Slide off the fusible link.
18. Remove the fan assembly (4 screws)
and install it on the new heat exchanger.
(Figure 82)
705i (ASME)
80 erugiF 79 erugiF
19. Install the largest O-ring (included in kit)
over the water outlet tube and the two
smaller O-rings (included in kit) over the
water inlet tubes. (Figure 82)
20. Slide the fusible link between the water
outlet and inlet tubes and onto the new
heat exch
21. Attach brackets at the back and side
holding the fusible link. Install the heat
exchanger hooking it on the brackets in
the back.
22. Install the 4 screws at the top and bottom
of the heat exchanger to the back of the
casing. (Figure 81)
23. Install the flue outlet vent (4 screws) and
seal plate (3 screws) and gasket at the
top of the water heater. (Figures 79 and 80)
anger. (Figure 82)
Top left screw Top right screw
Figure 81
Bottom screws
4 locations
On-Demand Gas Tankless Water Heater Service Manual
Figure 82
53
Water outlet tube
Water inlet tubes
Component Replacement Instructions
Heat Exchanger
24. Insert the burner and place the burner
cover plate into position. Attach the
burner cover plate first with 9 screws and
then attach the burner with 2 screws.
(Figure 78)
25. Replace the electrode gasket. (Figure 83)
26. Make sure that the black gasket (Figure 84)
is intact on the gas control assembly.
Replace the lower and upper gaskets
(included in kit) for the manifold plate
removing any residue. (Figure 85)
27. Attach the electrical connector to the
ignitor on the manifold and attach the gas
manifold with 2 machine screws at the
gas control assembly. (Figure 77)
28. Attach the gas manifold with 5 screws at
heat exchanger. (Figure 77)
705i (ASME)
Figure 83 Electrode Gasket
Gasket
29. Connect wire harness attachments.
30. Attach the ignition line at the burner
cover plate.
31. Attach the 3 electrical connectors to the
solenoid valves.
32. Attach the wire
assembly (white, yellow, black, red
wires).
33. Attach the brackets to the water line
connections. (Figure 77)
34. Install the front panel using 4 screws.
35. Turn on the water supply, power supply,
and gas supply.
36. Check for gas leaks.
harness to the fan
Figure 84
Figure 85
Gaskets
On-Demand Gas Tankless Water Heater Service Manual
54
Gas Pressure Setting Procedure
CAUTION
Do not touch the areas at or near the heat
exchanger or combustion chamber. These areas
become very hot and could cause burns.
1. Remove the front panel (four screws).
2. Calibrate the low fire and high fire settings as follows:
A. Remove the allen head plug and attach the manometer to the burner test point located
on the gas control (Figure 86 or 87).
Figure 86 Potentiometer (POT)
Burner test point Dip switches (SW1)
100/101 and 200/201 Series
Models 305e/o, 305i, 505e/o, 505i
Figure 87
Burner test point Dip switches (SW1)
100/101 and 200/201 Series
Models 705e/o (ASME), 705i (ASME)
Potentiometer (POT)
On-Demand Gas Tankless Water Heater Service Manual
55
Gas Pressure Setting Procedure
B. Turn on the gas supply.
C. Turn on the power supply.
D. Flow water through the water heater at the
maximum flow rate obtainable. (At least 3
gallons per minute is recommended.)
E. Move No. 7 dip switch of the SW1 bank to the
ON position to calibrate “Forced Low”
combustion. (Figure 89)
F. Check the burner test point pressure.
G. Remove the rubber access plug (Figure 88) and
adjust the regulator screw on the modulating
valve to obtain the correct low fire manifold
pressure. Refer to the data plate on the unit.
Install rubber access plug.
H. Move No. 7 and No. 8 dip switches of the SW1
bank to the ON position to calibrate “Forced
High” combustion. (Figure 90)
I. Check the burner test point pressure.
J. Adjust the high pressure Potentiometer (POT)
(Figure 86 or 87) on the PC Board to obtain the
correct high fire manifold pressure. Refer to the
data plate on the unit.
K. Move No. 7 and No. 8 back to the OFF position
to return the appliance to “Normal” combustion.
(Figure 91)
L. Close hot water taps.
M. Turn off gas supply and 120 V power supply.
N. Remove manometer and re-install allen head
plug.
Figure 88
Figure 89
Forced Low
Figure 90
Forced High
Access plug
Switch No.
ON
O
1
F
2
F
3
4
5
6
7
8
Switch No.
ON
O
1
F
2
F
3
4
5
6
7
8
O. Turn on the gas supply and 120 V power
supply.
P. Operate the unit and check for gas leaks.
3. Install the front panel using four screws.
On-Demand Gas Tankless Water Heater Service Manual
56
Figure 91
Normal
Switch No.
ON
O
F
F
1
2
3
4
5
6
7
8
Manifold Gas Pressure Settings
100/101 and 200/201 Series
Natural Gas Propane Gas
(Inch - W.C.)
(Inch - W.C.)
305e/o
505e/o
705e/o (ASME)
305i
505i
705i (ASME)
Altitude High Fire Low Fire High Fire Low Fire
2.9 0.56 4.2 0.88
3.3 0.56 5.1 0.88
2.8 0.65 3.8 0.80
less than 10200 ft
(3109 m)
2.7 0.52 4.4 0.92
3.3 0.52 5.0 0.92
3.0 0.67 3.7 0.83
On-Demand Gas Tankless Water Heater Service Manual
57
100/101 and 200/201 Series
Dip Switch Settings
SW1 Bank
OFF - “Long Flue”
ON - “Short Flue” and Outdoor Models
1
2
3
0-2000 ft
(0-610 m)
#2: OFF #2: OFF #2: ON #2: ON
#3: OFF #3: ON #3: OFF #3: ON
4
5
6 OFF position
“Long flue” is defined as:
0 elbows and length is greater than 21 ft
1 elbow and length is greater than 15 ft
2 elbows and length is greater than 9 ft
Settings dependent on altitude
2001-5200 ft
(610-1585 m)
OFF - if using standard controller
OFF - 120ºF default temperature without a
controller
ON - 140ºF default temperature without a
controller
5201-7700 ft
(1585-2347 m)
7701-10200 ft
(2347-3109 m)
SW2 Bank (present on replacement PC boards only)
OFF - Propane Gas
1
ON - Natural Gas
OFF - Outdoor model
2
ON - Indoor model
OFF - 305e, 305i, 505e, 505i, 705e/o (ASME),
3
705i (ASME)
OFF - 505e/o, 505i, 705e/o (ASME), 705i (ASME)
4
ON - 305e/o, 305i
OFF - 305e, 305i, 505e, 505i,
5
6 OFF position
705e/o (ASME), 705i (ASME)
OFF position - Used for low fire and high fire
7
settings. Refer to the gas pressure setting
8
procedure.
On-Demand Gas Tankless Water Heater Service Manual
58
Notes
On-Demand Gas Tankless Water Heater Service Manual
59
• 500 Tennessee Waltz Parkway • Ashland, TN 37015 •
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