A.O. Smith ATI-140H-N How to use

Condensing Models
On-Demand Water Heater
Service Handbook
100267626
January 2016
MODELS:
ATI-140H-N GTS-140-NIH GT-140-NIH T-H3M-DV-NG
ATI-140H-P GTS-140-PIH GT-140-PIH T-H3M-DV-LP
ATO-140H-N GTS-140-NEH GT-140-NEH T-H3M-OS-NG
ATO-140H-P GTS-140-PEH GT-140-PEH T-H3M-OS-LP
THIS SERVICE HANDBOOK IS FOR USE BY QUALIFIED SERVICE PROFESSIONALS ONLY.
IF YOU NEED ASSISTANCE, CALL TECHNICAL SUPPORT AT 877-737-2840.

2 • Condensing Models: On-Demand Water Heater Service Handbook
TABLE OF CONTENTS
Specifications.................................................................................................................................................................................................................4
Introduction...................................................................................................................................................................................................................5
General Installation Guidelines .....................................................................................................................................................................5
Normal Operation .........................................................................................................................................................................................................6
Activation ......................................................................................................................................................................................................6
Operation ......................................................................................................................................................................................................6
Shutdown ......................................................................................................................................................................................................6
Troubleshooting ............................................................................................................................................................................................................7
Preliminary Checklist .....................................................................................................................................................................................7
Gas/Water/Electric: ...................................................................................................................................................................... 7
Remote Controller: ....................................................................................................................................................................... 7
High Altitude: ................................................................................................................................................................................ 7
Long Vent Run................................................................................................................................................................................ 7
Hard Water: .................................................................................................................................................................................. 7
New Installations: ......................................................................................................................................................................... 7
External Problem: ......................................................................................................................................................................... 7
Next Step: ..................................................................................................................................................................................... 7
General Issues ...............................................................................................................................................................................................7
Water is not hot enough. .............................................................................................................................................................. 7
Water is too hot. ........................................................................................................................................................................... 8
Temperature fluctuates when a fixture is opened......................................................................................................................... 8
Unit does not ignite when water goes through it.......................................................................................................................... 9
Abnormal sounds come from the unit.......................................................................................................................................... 9
Error Codes..................................................................................................................................................................................................10
Incorrect DIP Switch Settings ...................................................................................................................................................... 12
Abnormal Combustion ................................................................................................................................................................ 12
Ignition Failure / Flame Loss ....................................................................................................................................................... 12
Outlet Thermistor Failure ........................................................................................................................................................... 13
Inlet Thermistor Failure ............................................................................................................................................................. 13
Exhaust Thermistor Failure ........................................................................................................................................................ 14
Air-Fuel Ratio Rod Failure ........................................................................................................................................................... 14
Abnormal Solenoid Gas Valve .................................................................................................................................................... 14
Abnormal Fan Motor .................................................................................................................................................................. 15
False Flame Detection ................................................................................................................................................................ 16
Remote Control Problem ............................................................................................................................................................ 16
Abnormal Exhaust Temperature ............................................................................................................................................... 17
Abnormal Combustion ............................................................................................................................................................... 17
Dip Switch Settings ......................................................................................................................................................................................................19
Wiring Diagram............................................................................................................................................................................................................22

Condensing Models: On-Demand Water Heater Service Handbook • 3
BASICS
BASICS
Service Procedures......................................................................................................................................................................................................24
Verifying DIP Switch Settings .......................................................................................................................................................................24
Unit Draining and Filter Cleaning.................................................................................................................................................................24
Checking for a Crossed Connection .............................................................................................................................................................25
Checking for a Reversed Connection ...........................................................................................................................................................25
Checking Inlet Gas Pressure/Purging Air from Gas Line ..............................................................................................................................25
Checking and Adjusting the Manifold Gas Pressure ....................................................................................................................................25
Adjusting Minimum Manifold Pressure ....................................................................................................................................... 26
Checking the Overheat Cutoff Fuse (OHCF).................................................................................................................................................27
Checking the Flow Sensor............................................................................................................................................................................27
Cleaning the Rod Assembly (Flame Sensor and Air/ Fuel Ratio Rod) ..........................................................................................................28
Descaling the Unit .......................................................................................................................................................................................29
Draining and Hose Connection .................................................................................................................................................... 29
Pump And Descale ...................................................................................................................................................................... 29
Cleanse the System ..................................................................................................................................................................... 29
Cleaning the Combustion Components.......................................................................................................................................................29
Maintenance ..............................................................................................................................................................................................................35
Replacing the Heat Exchanger (Indoor Models) ..........................................................................................................................................37
Removing Heat Exchanger Components (Indoor Models)...........................................................................................................................37
Preparing the New PRIMARY Heat Exchanger for Installation (Indoor Models).........................................................................................40
Preparing the New SECONDARY Heat Exchanger for Installation (Indoor Models) .....................................................................................41
Installing the Heat Exchanger (Indoor Models) ..........................................................................................................................................41
Replacing the Heat Exchanger (Outdoor Models) .......................................................................................................................................46
Removing Heat Exchanger Components (Outdoor Models)........................................................................................................................46
Preparing the New PRIMARY Heat Exchanger for Installation (Outdoor Models)......................................................................................49
Preparing the New SECONDARY Heat Exchanger for Installation (Outdoor Models).................................................................................50
Installing the Heat Exchanger (Outdoor Models) .......................................................................................................................................50
Flow Sensor/Control Valve Removal and Installation .................................................................................................................................55
Removal ...................................................................................................................................................................................... 55
Installation .................................................................................................................................................................................. 55
Burner Removal and Installation .................................................................................................................................................................56
Removal ..................................................................................................................................................................................... 56
Installation .................................................................................................................................................................................. 59
Gas Valve/Manifold Plate: Removal and Installation...................................................................................................................................61
Removal ...................................................................................................................................................................................... 61
Installation .................................................................................................................................................................................. 62
Component Diagrams/Item Numbers .........................................................................................................................................................................67
Component Item Numbers..........................................................................................................................................................................................71

4 • Condensing Models: On-Demand Water Heater Service Handbook
BASICS
Table 1: 140 (T-H3M) Direct Vent Indoor and Outdoor*
Model 140 lndoor
(T-H3M-DV)
140 Outdoor
(T-H3M-OS)
Natural Gas Input
(Operating Range) BTU/h Min.: 15,000 Max.: 120,000
Propane Input
(Operating Range) BTU/h Min.: 15,000 Max.: 120,000
Gas Connection 1/2” NPT
Water Connection 3/4” NPT
Water Pressure* psi (MPa) 15 - 150 (0.1 - 1.0)
Natural gas lnlet Pressure inch W.C. (kPa) Min. 5.0 (1.2)
Max. 10.5 (2.6)
Propane lnlet Pressure inch W.C. (kPa) Min. 8.0 (2.0)
Max. 14.0 (3.5)
Manifold
Pressure**
Natural Gas inch W.C. (kPa) Min. 1.3 (0.32)
Max. 3.3 (0.82)
Min. 1.3 (0.31)
Max. 2.0 (0.50)
Propane inch W.C. (kPa) Min. 1.1 (0.28)
Max. 3.0 (0.75)
Min. 1.1 (0.27)
Max. 1.6 (0.40)
Weight lbs. (kg) 50 (22.5) 50 (22.5)
Dimension inch H 21·3/4 x W 14 x D 9·1/4
mm H 552 x W 352 x D 236
Ignition Electric Ignition
Electric
Supply VAC/ Hz 120/60
Consumption
Operation W/A 53.9/0.7
Standby W/A 3.2/0.05
Freeze-
Protection W/A 223.9/1.94
* 40 psi (0.27 MPa) or above is recommended for maximum flow.
** The Manifold Pressure is the factory setting and should not need adjustment. NOTE: Manifold Pressure readings
are taken with the front cover removed.
NOTE:
• Check the rating plate to ensure this product matches your specifications.
• ln accordance with ANSI Z21.10.3, CO emission does not exceed 400 PPM for normal input.
• The manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and
without incurring obligation.
SPECIFICATIONS

Condensing Models: On-Demand Water Heater Service Handbook • 5
BASICS
INTRODUCTION
Read and follow all safety messages
and instructions in this handbook and
on the product labeling.
This is the safety alert
symbol. It is used to alert
you to potential physical
injury hazards. Obey all safety
messages that follow this symbol to
avoid possible property damage,
serious injury or death. Do not remove
any permanent instructions, labels, or
the rating plate from either the outside
of the water heater or on the inside of
the access panels.
DANGER indicates a hazardous
situation that, if not avoided, will
result in death or serious injury.
WARNING indicates a hazardous
situation that, if not avoided, could
result in death or serious injury.
CAUTION indicates a hazardous
situation that, if not avoided, could
result in minor or moderate injury.
NOTICE indicates practices not
related to physical injury.
WARNING!
●Installation and service must be
performed by a qualified installer
(such as a licensed plumber or gas
fitter). Otherwise, the warranty
will be void.
●The installer/service agent
(licensed professional) is
responsible for correctly installing
or servicing your water heater and
for compliance with all national,
state/provincial, and local codes.
This handbook provides the necessary
information for troubleshooting the
140/T-H3M tankless water heaters.
It will be effective in helping your
troubleshooting needs as long as
the instructions are followed in the
intended order. Here is how to use
this manual:
●First, refer to the 140/T-H3M
Installation Manual as the primary
source of information. Refer to it
along side this manual throughout
the troubleshooting process.
●Before troubleshooting, if you are
unfamiliar with how a tankless unit
operates, read “Normal Operation”
on page 6.
●To double-check or troubleshoot
a new installation, use the
140/T-H3M installation manual.
●When beginning troubleshooting,
first go through the “Preliminary
Checklist” on page 7. It is
designed to fix the most common
and frequent problems and
provide you with background
information to help narrow down
the information you need.
●If you have received an error code,
refer to “Error Codes” on page
10. If you have not received
an error code, refer to “General
Issues” on page 7.
●Consider removing the following
sections from this manual for easy
reference:
• “Component Diagrams/Item
Numbers” (starting on page
67).
• The following graphics, which
show the location of basic
components.
◦Indoor models:
Page 35, Figure 24.
◦Outdoor models:
Page 36, Figure 25.
This will allow you to lay the
loose pages beside this manual
for easier reference.
If you have any problems or
questions regarding this equipment,
or at any point become confused
or uncomfortable with any of the
procedures, consult the technical service
department or the local service agent.
General
Installaon
Guidelines
1. Follow all local codes, or in the
absence of local codes, follow the
current edition of the National Fuel
Gas Code: ANSI Z223.1/NFPA 54 in
the USA or B149.1 (Natural Gas and
Propane Installation Code) in Canada.
2. Properly ground the unit in
accordance with all local codes
or, in the absence of local codes,
with the National Electrical Codes:
ANSI/NFPA 70 in the USA or CSA
standard C22.1, Canada Electrical
Code, Part 1 in Canada.
3. Carefully plan where you intend to
install your water heater.
4. Check the rating plate for the
correct GAS TYPE, GAS PRESSURE,
WATER PRESSURE and ELECTRIC
RATING. See Figure 1. NOTE:
If this unit does not match your
requirements, do not install.
If any problem occurs, turn off all hot
water taps and turn off the gas. Then
call a trained technician or the gas
company.
Figure 1.
ZĂƟŶŐ
Plate

6 • Condensing Models: On-Demand Water Heater Service Handbook
BASICS
Becoming familiar with how a tankless
water heater normally operates may
help to troubleshoot it. Assuming it
is properly installed with appropriate
gas, water, and electrical connections,
it should operate as follows:
Acvaon
1. A hot water tap is opened. The
flow sensor detects a flow rate
through the heater that is greater
than the 0.5 GPM activation point.
The system also verifies that the
temperature difference between
the incoming water and the set
temperature is great enough
to meet the 15,000 BTUH input
requirement.
2. The fan activates after the
conditions in the previous step are
met.
3. Igniter activates. You can hear the
buzzing of the spark igniter.
4. The main gas valve, proportional
valve, and solenoid gas valves will
open. You will hear a deep “clunk
clunk” noise.
5. Once a flame is detected, the green
“In Use” LED will activate. (This green
LED is located on the temperature
controller or remote controller.)
Operaon
1. The proportional gas valve and
fan will modulate based on the
amount of hot water demanded
and the temperature rise needed.
2. You may notice that only partial
sections of the burner will be lit.
This is normal operation. There
are three sections on the burner
assembly, and the computer
controls the number of sections
needed based on the flow rate
and temperature rise required.
3. The water control valve within the
unit may restrict water flow to
ensure that the set temperature
will be met.
Shutdown
1. The heater will shut down when
the water flow rate drops below
the deactivation point of 0.4 GPM.
2. The heater will close the main
gas valve and solenoid gas valves,
then extinguishing the flame.
3. When the flame disappears, the
green “In Use” LED will turn off.
4. The fan will increase in speed
to purge the venting of any
remaining exhaust gases. The
length of post-purge can last up to
1 ½ minutes.
5. The heater goes into standby and
waits for the process to begin
again.
NORMAL OPERATION
Figure 2. The purpose of this diagram is to illustrate tankless water
heater design concepts, and may not be accurate to the
unit’s physical description.
Burners
Exhaust
Secondary
heat exchanger
Primary
heat exchanger
Igniter
Gas valve
Fan motor
Flow sensor
Condensate
drain port
Gas inlet
Cold water inlet
Thermistor
Hot water outlet
Thermistor
Intake port
Exhaust
Thermistor
Water control
valve
Computer
board (PCB)

Condensing Models: On-Demand Water Heater Service Handbook • 7
TROUBLESHOOTING
TROUBLESHOOTING
Preliminary
Checklist
To get started, review the following
topics. You may also refer to “General
Issues,” if necessary.
Gas/Water/Electric:
• The gas supply valve should be
fully open and the gas line purged.
• Verify that the correct gas type
is being used. Check the supply
gas, the gas type dip switch, and
the gas type shown on the rating
plate. All three must agree in
terms of gas type, and your water
heater model must be designed
for use with that type of gas
(natural gas or LP).
• The water supply valve should be
fully open.
• The unit should be connected to
a 120 VAC 60 Hz power supply.
When the heater is in Stand By,
the green LED on the computer
board will be lit and the amber
LED on the temperature/remote
controller will be lit.
• If the power switch inside the
unit is turned off, then the LEDs
mentioned above will be off.
Remote Controller:
If you are using a remote controller,
the remote’s power button must be
turned on. The amber Stand-By LED
will be lit.
High Altude:
Is your location at an altitude of over 2,000
feet? This may cause a lack of air. See
“Dip Switch Settings,” page 19.
Long Vent Run
Do you have a long vent run? You
may see an unnecessary error due to
back pressure in the venting. See “Dip
Switch Settings,” page 19.
Hard Water:
What is the hardness of the water?
A means of reducing scale is always
recommended, but if the water is
above 7 grains of hardness or 70-
140 ppm, one must be installed. If
there isn’t anything installed, existing
installations will gradually accumulate
scale buildup on the heat exchanger
and cause a leak. Heat exchanger
leaks due to hard water scale are not
covered under the warranty.
New Installaons:
A new installation that does not
function properly is most likely caused
by reverse plumbing or a dirty inline
water filter.
External Problem:
• Test whether the problem is
within the unit or external to the
unit (i.e., in the plumbing system)
by attempting to run hot water
locally through the isolation valve.
Ensure that the hot water shutoff
is closed while running water
through the hot isolation valve
drain port.
• Does the heater ignite and remain
running properly? Or does the
heater shut down with an error
code? If it runs well through the
hot isolation valve, the plumbing
system is at fault.
Next Step:
Finally, check to see if the unit has an error
code. The error code will be displayed on
the temperature controller (or remote
controller) and by flash codes on the green
LED on the computer board. See Figure 3,
page 10. See also the error code chart
on page 10.
• If it is displaying an error code, proceed
to “Error Codes” on page 10.
• If there is no error code, proceed
to “General Issues.”
General Issues
Proceed to the “Error Codes” section
if an error code is identified. For other
common problems that do not involve
error codes, see if the following items
help:
Water is not hot enough.
• What is the set temperature of
the heater? Temperature can be
adjusted using the temperature or
remote controller.
◦Isolate the heater by closing
the hot isolation valve. Open
the hot drain valve and test
the heater. A hose may need
to be connected to the hot
drain prior to opening it in
order to drain the water
properly.
◦If the temperature and flow
rate are correct through the
drain, then the problem

8 • Condensing Models: On-Demand Water Heater Service Handbook
TROUBLESHOOTING
resides in the plumbing line,
not in the tankless unit.
• Check for crossed plumbing between
cold water lines and hot water lines.
See the “Service Procedures” section
for instructions.
• Unit may be hard water scaled.
The scale acts as an insulator
preventing the heat exchanger
from transferring heat to the
water. Refer to “Descaling the
Unit,” page 29.
• The unit may not be receiving
enough gas.
◦The gas supply valve may not
be fully open.
◦The gas line may be sized
improperly.
◦The gas supply pressure
may be too low. This may be
caused by a malfunctioning
gas supply regulator, so
check to see if the regulator
is working properly. See
“Check gas supply” later in
this section.
• If a recirculation system is
installed, ensure that a check
valve is installed between
the pump discharge and the
connection to the cold water
supply. Inspect the check valve
for proper operation. If there
isn’t one installed, or if it is
malfunctioning, cold water may
be back-feeding into the system.
• If a mixing valve is installed, check
to see if it is operating properly
and not allowing water to cross
over.
• A 101 error code will reduce the
amount of gas input into the
heater. If the heater is displaying
a 101 error code, see “Abnormal
Combustion” on page 12.
• Output temperature will be
affected if air flow is impeded.
◦Check for construction dust
and debris in venting, such as
dry wall dust.
◦If there is dust inside the
cabinet, there will also be
dust inside the burner and
heat exchanger. Refer to
“Cleaning the Combustion
Components,” page 29.
Water is too hot.
• The temperature setting
may be set too high. Adjust
the temperature using the
temperature controller or the
remote controller.
• The flow adjustment valve could
be obstructed due to hard water
scale or debris, causing lower than
expected water flow. Verify water
flow with a graduated container
or with the remote temperature
controller, if one is installed.
• The output thermistor could be
compromised. This component
may be checked by entering
the Diagnostics Mode on the
remote controller or temperature
controller. Turn power off to the
unit and run cold water through
it; check to see if the inlet and
outlet temperatures read the
same on the remote. Press the
INFO button once on the temp/
remote controller. The inlet water
temperature will be displayed.
Press the INFO button again to
show the outlet temperature. If
the readings are not similar, then
one of the thermistors may not
be reading correctly. Refer to
error codes 311 and 321 in “Error
and Flash Codes” (p. 10).
Temperature fluctuates when a
fixture is opened.
Make sure that the unit is installed
properly.
• Test whether the problem is
within the unit or external to the
unit (i.e., plumbing system).
• Plumbing connections:
1. Check for a crossed
connection. See “Checking
for a Crossed Connection,”
page 25.
2. Problems with the
recirculation system:
◦Make sure that a
check valve is installed
between the pump
discharge and the
connection to the cold
water supply.
◦Check to see if the pump
is operating properly.
◦Check for air cavitation.
If present, the pump
will be very hot or
chattering.
◦Check the directional
indicator on the pump
flange.
◦Check the sizing of the
pump. A minimum flow
of 2 gpm is required.
• Check gas supply:
◦Verify that the gas meter
is capable of supplying
sufficient gas supply to all
gas appliances. Determine
the sum of all gas appliances’
maximum energy input (in
cubic feet per hour). This
number must be less than
the maximum ratings shown
on the gas meter’s rating

Condensing Models: On-Demand Water Heater Service Handbook • 9
TROUBLESHOOTING
plate. If the maximum
energy input of all appliances
exceeds the maximum rating
of the gas meter, consult
your local gas utility.
◦For LP models, there may
not be enough gas left in the
propane tank.
◦Verify that the supply
gas pressure is within
specification, not only when
the heater is in standby,
but also while the heater is
running on maximum fire.
(See “Checking Inlet Gas
Pressure/Purging Air from
Gas Line” on page 25.)
◦The gas supply pressure
may be too low. This may be
caused by a malfunctioning
gas supply regulator.
◦Check the pressure difference
between static and maximum
operating pressure. If the
drop is more than 1 inch W.C.,
there may be insufficient gas
supply. NOTE: In Canada, do
not exceed the maximum
allowable pressure drop
permitted by B149.1.
• Venting:
◦Verify that the venting is
installed to manufacturer’s
specifications.
◦Verify that the vent run
does not exceed the
allowable limit. Refer to
the installation manual.
◦Verify that the DIP switch
settings for vent length
match the installation’s
equivalent vent length and
diameter.
• The filter on the cold water inlet
should be clean. Look for signs of hard
water scaling. See “Unit Draining and
Filter Cleaning” (p. 24).
• If the clear tube from the
proportional gas valve to the
bottom of the combustion
chamber is disconnected,
fluctuations in temperature and/
or very low flow to the fixtures
may occur.
• On well systems or even on
some city water systems, water
pressure fluctuations (especially
on low flow) of 8 to 10 psi will
result in flow rate fluctuations.
This may result in minor
temperature fluctuations.
• Flow sensor or water control
valve may be compromised.
Inspect both parts for blockages
or debris.
Unit does not ignite when
water goes through it.
• If you use the remote controller,
is the remote power button
turned on?
• Check to see if the Computer
board is receiving power. This
can be verified by observing
the green LED on the computer
board or the amber LED on the
temperature/remote controller.
If it is not lit, the computer board
is not being powered. Check to
see if the ON/OFF switch below
the fuse box is set to the on
position, or if the fuse in the fuse
box assembly is blown.
• Is the flow rate over 0.5 gpm?
See if the unit initiates when you
increase demand of water being
drawn through the unit (e.g.,
opening up more hot fixtures).
You can verify the flow rate by
pressing the info button on the
front of the unit until the arrow
lights up beside “flow.”
• If the unit is in a recirculation
system, the return water
temperature may be too close
to the set point temperature
to activate the water heater.
You can verify the incoming
water temperature by using the
information button on the front
of the unit.
• Check that the gas line is open
and is purged of air (page 25).
• Check that the filter on the cold
water inlet is clean (page 24).
• Check for a reversed connection of
the plumbing to the water heater
or a crossed connection in the
plumbing system. See page 25.
• Check for problems with the
recirculation system.
Make sure that a check valve
is installed between the pump
discharge and the connection
to the cold water supply. A
malfunctioning or missing
check valve will cause a cross
connection, allowing cold water
to back-feed into the system.
• If the fan does not initiate at
all and it is verified that there
is power to the unit, the flow
sensor may not be working
properly. Check the flow sensor
for proper impeller functionality.
Abnormal sounds come from
the unit.
• Check the fan for debris.
◦Check for blockages in the
exhaust vent and intake air
line.
◦Check for proper gas supply
pressure.
• Contact the technical service
department.

10 • Condensing Models: On-Demand Water Heater Service Handbook
TROUBLESHOOTING
Error Codes
All units have self-diagnostics for safety and convenience when troubleshooting.
If there is a problem with the unit, a numerical error code will display on the TM-RE42 Remote Controller (if installed) or on
the temperature controller of indoor models. Installation-related problems may also produce an error code. If the remote/
temperature controllers are not working, the green LED on the computer board will flash a code pattern. (The green LED is located
just above the DIP switches as shown in Figure 3.)
Table 2: Error and Flash Codes
ERROR CODE GREEN LED ON
COMPUTER BOARD
SYMPTOM OR ISSUE TROUBLESHOOTING PROCEDURE
031 One Flash Incorrect DIP switch setting Incorrect DIP Switch Settings, p. 12.
101 Five Flashes Abnormal Combustion
(lockout is imminent)
Abnormal Combustion, p. 12.
111 or 121 Three Flashes Ignition failure / Loss of flame Ignition Failure / Flame Loss, p. 12.
311 Two Flashes Outlet thermistor failure Outlet Thermistor Failure, p. 13.
321 Two Flashes Inlet thermistor failure Inlet Thermistor Failure, p. 13.
341 Two Flashes Exhaust thermistor failure
(indoor models only)
Exhaust Thermistor Failure, p. 14.
391 Two Flashes Air-fuel ratio rod failure Air-Fuel Ratio Rod Failure, p. 14.
Figure 3. Green LED on Computer Board Figure 4. TM-RE42 Remote Controller
(Continued on next page.)