Takagi T-K2 User manual

W
ARNING
This product must be installed and
serviced by a licensed plumber, a
licensed gas fitter, or a professional
service technician and/or in accordance
with all local code. Improper installation
and/or operation, or installation by an
unqualified person, will void the warranty.
W
ARNING
Operation of this unit creates carbon
monoxide gas and flue gases which can
cause serious injury or death. In addition,
if the information in this manual is not
followed exactly, a fire or explosion may
result causing property damage, personal
injury or death.
T-K2 Instantaneous Water Heater
Installation Manual and Owner’s Guide
Flash Water Heater
Model T-K2
Suitable for potable water heating and space heating
FEATURING
•ENDLESS HOT WATER
•ON DEMAND
•COMPACT, SPACE SAVING
•ENERGY CONSERVING
•COMPUTER CONTROLS
•COMPUTERIZED SAFETY
•NO PILOT LIGHT
Takagi Industrial Co. USA Inc.
3-B Goodyear
Irvine, CA 92618
Toll Free [phone] USA
Toll Free [phone] CANADA
www.Takagi.com

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CONTENTS
Specification …………. 2
Introduction …………..3
For your safety …………..3-4
Installation …………. 5
•General …………. 5
•Accessories …………. 5
•Outdoor Installation ………….5-6
•Indoor Installation ………….6-7
•Venting Instructions …………..7 -9
•Gas Supply/Gas Pipe sizing………..10-11
•Water Connection …………. 11-12
•Electrical Connection …………. 12
•Initial operation …………. 13
Normal operation …………. 13
•Flow …………. 13-14
•Temperature setting …………. 14
•Freeze Protection Device …………. 14-15
•Maintenance and Service …………..15-16
•Error codes …………..16
Wiring diagram …………..17
For your Safety …………..18
Danger …………..19
Application …………..20
•Space Heating …………..20
•Dual-purpose heating …………..21
•Storage Tank …………..22
•Re-Circulation …………..22
Optional Items …………..23
Component Diagram …………24-26
Component Diagram …………..27
Output temperature Chart …………..28
SPECIFICATIONS
Natural Gas Input Min. 20,000 Btu
Max. 185,000 Btu
LPG Input Min. 19,000 Btu
Max. 175,000 Btu
Gas Connection ¾” NPT
Water Connections ¾” NPT
Water Pressure Min. 15 psi
Max. 150 psi
Natural Gas Pressure Inlet Min. 5” WC
Max. 10.5” WC
LP Gas Pressure Inlet Min. 11” WC
Max. 14” WC
Manifold Pressure Natural 2.3” WC
Propane 2.5” WC
Weight 60 lbs.
Dimensions 24.5”x16.5”x8.3”
Ignition Electronic Ignition
Electrical Supply AC 120 V
*** NOTE ***
•Check the rating plate to ensure this
product matches your specifications;
•Before installing in areas over 4,500 feet
above sea level, contact Takagi;
•Takagi is constantly improving its products
therefore specifications are subject to
change without prior notice.

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INTRODUCTION
This manual provides information necessary
for the installation, operation, and maintenance
of the Model T-K2 water heater. This unit
includes a fan enabling sidewall (power)
venting and an advanced electronic ignition
system.
The model description is listed on the rating
plate which is attached to the front cover of the
water heater. Please read all installation
instructions completely before installing this
product. If you have any problems or
questions regarding this equipment, consult
with Takagi or its local representative.
Experiences have shown that most operating
problems are caused by improper installation.
The T-K2 Water Heater is an instantaneous,
tankless water heater designed to supply
endless hot water to your entire household
and/or commercial facility utilizing total
efficiency. The principle behind the T-K2 Water
Heater is simple. Once you open a hot water
tap, water flows through the T-K2 Water
heater. Once a minimum of 0.75 GPM is
achieved, the flow sensor automatically
commands the computer to turn on the fan,
activate the electronic igniter and open the gas
valves. The computer monitors water
temperature, water flow rate and gas flow to
ensure that you get the right amount of hot
water at the correct hot water temperature.
After the burners are ignited, the “fire on” lamp
is lit. The computer will modulate the gas
supply valve and water flow. 0.75 gallons per
minute is required to turn the burners on; after
the burners are ignited, the flow rate can be
lowered to 0.6 gallons per minute to maintain
the heater on. It is advisable to open further
the cold tap rather than decreasing the hot tap
to adjust the water temperature. As long as
you have water, gas and electricity, you will get
an endless flow of hot water. Open a hot water
tap to turn on your water heater. Close the tap
to turn off your water heater.
FOR YOUR SAFETY
PLEASE READ THIS MANUAL CAREFULLY
AND FOLLOW ALL DIRECTIONS.
1. Follow all local codes, or in the absence of
local codes, follow the most recent edition
of the National Fuel Gas Code, ANSI
Z223.1/NFPA 54 in the USA or the
CAN/CSA 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 T-K2 Water Heater. Ensure that your
heater will have enough combustible air
and proper ventilation and locate your
heater where water leakage will not do
damage to surrounding areas. If there is a
possibility of water damage, install a
suitable drain pan under the unit which will
not restrict combustible airflow.
4. Check the rating plate for the correct gas
type, gas pressure, water pressure and
electrical rating. If this unit does not match
your requirements, do not install.
The installer is responsible for the correct
installation of your Flash T-K2 Water
Heater. Installation and service must be
performed by a qualified installer (for
example, a licensed plumber or gas fitter)
otherwise the warranty by Takagi will be
void.
Rating plate

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5. If any problem should occur, turn off all hot
water taps and turn off the gas. Then call a
trained technician or the Gas Company or
the manufacturer.
6. WARNING: Do not disconnect the
electrical supply if the ambient temperature
will drop below freezing. The Freeze
Prevention Device only works if the unit
has electrical power. The Freeze
Prevention Device is rated for temperatures
down to 5 ºF (-15 ºC) in a wind free
environment. Refer to the section on
Winterizing and the Freeze Prevention
Device for more information. The Warranty
will not be covered if the heat exchanger is
damaged due to freezing.
7. WARNING: Water temperatures over
125ºF can cause severe burns instantly or
death from scalding. The water
temperature is set at 122ºF (50ºC) from the
factory to minimize any scalding risk.
Before bathing or showering always check
the water temperature.
8. WARNING: Do not use this appliance if
any part has been in contact with or been
immersed water. Immediately call a trained
technician to inspect and/or service the unit
if necessary.
9. WARNING: Do not store or use gasoline or
other flammables, vapors or liquids in the
vicinity of this appliance.
10. WARNING: Do not reverse the water
and/or gas connections as this will damage
the gas valves and can cause severe injury
or death. Following the diagram below
when installing your water heater:
GENERAL
The T-K2. Water Heater is an instantaneous,
tankless water heater designed to supply
endless hot water to your entire household
and/or commercial facility utilizing total
efficiency. The principle behind the T-K2 Water
Heater is simple. Once you open a hot water
tap, water flows through the T-K2 Water
heater. Once a minimum of 0.75 GPM is
achieved, the flow sensor automatically
commands the computer to turn on the fan,
activate the electronic igniter and open the gas
valves. The computer monitors water
temperature, water flow rate, and gas flow to
insure that you get the right amount of hot
water at the correct hot water temperature.
After the burners are ignited, the “fire on” lamp
is lit. The computer will modulate the gas
supply valve and water flow 0.75 gallons per
minute is required to turn the burners on;, after
the burners are ignited, the flow rate can be
lowered to 0.6 gallons per minute to maintain
the heater on. It is advisable to increase the
cold tap rather than decreasing the hot tap to
adjust the water temperature. As long as you
have water, gas and electricity, you will get an
endless flow of hot water. Open a hot water tap
to turn on your water heater. Close the tap to
turn off your water heater.

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INSTALLATION
GENERAL
All gas water heaters require careful and
correct installation to ensure safe and efficient
operation. This manual must be followed
exactly. Read the “For Your Safety” section at
the beginning of this manual.
1. The gas regulator is preset at the
factory; it is computer controlled and
should not need adjustment;
2. Maintain proper space for servicing.
Install the unit so that it can be
connected or removed easily;
3. The electrical connection requires a
means for switching off the power
supply;
4. If you will be installing the unit in a
contaminated area with a high level of
dust, sand, flour, aerosols or other
contaminants, they can become
airborne and enter and buildup within
the fan and burner causing damage to
the unit. The warranty will not cover
damage caused to the unit due to
installation in a contaminated
environment that has not been
converted.
5. Particles from these objects may clog
the air vent or reduce the functions of
the rotating fan and cause improper
burning of the gas. Regular
maintenance is recommended for these
types of environment.
6. Do not install the unit where the
exhaust vent is pointing into any
opening in a building or where the
noise may disturb your neighbors.
Make sure the vent termination is 4 feet
from a doorway or opening to prevent
exhaust from entering.
7. Some chemicals used in a beauty salon
may affect the flame sensor. Water
heater may not work properly. Please
consult with Takagi, when the water
heater is installed in a beauty salon.
8. Water hardness may affect the water
heater. Water heater may be damaged.
The warranty will not cover damage
caused by water quality.
Accessories
Check that the installation manual, the
extension cable and the warranty card were
included with the unit.
OUTDOOR INSTALLATION
Follow all local codes, or in the absence of
local codes, follow the most recent edition of
the National Fuel Gas Code ANSI
Z223.1/NFPZ 54 in the USA or the CAN/CSA
B149.1 Natural gas and Propane installation
Code in Canada.
Ensure that the unit is set for outdoor
installation. The ‘OUT’ dipswitch on the
computer board should be switched to its ‘ON’
position:
The outdoor vent cap
must be used when
unit is installed
outdoor. Takagi
recommends the use
of its part No. TK-
TV04.
Locate the water
heater in an open,
unroofed area and
maintain the following
minimum clearances:
Indoor or Outdoor
dip switch setting

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Outdoor Installation Service Clearances
Left side of heater 12”
Front (Maintenance space) 24”
Back of heater 1”
Right side of heater 6”
Top of heater 36”
WARNING: Do not install this water heater under
an overhang less than 3 feet from its top or eaves.
The area under an overhang must be open to three
sides
WARNING: Do not have the vent terminal
pointing toward any opening into a building. Do
not locate your heater in a pit or location where
gas and water can accumulate.
WARNING: Do not install the heater where
water, debris or flammable vapors may get into
the flue terminal. This may cause damage to
the heater and void the warranty.
WARNING: Do not install the water heater
vent terminator within 1 foot in the USA and
within 3 feet in Canada of any air intake or
building opening.
INDOOR INSTALLATION
When installed indoors, the T-K2 water heater
shall be located in an area to maintain the
following minimum clearances around the unit:
Indoor Installation Service Clearances
Left side of heater 6”
Front (Maintenance space) 24”
Back of heater 1”
Right side of heater 2”
Top of heater 12"
The diagram below details the required
clearances around the unit:
Wall Hanging Installation
For a wall mount installation, use TK-BK01
brackets to securely attach the T-K2 to the
wall.
Locate the heater as desired, but follow all
applicable local codes, as well as the indoor or
outdoor clearances that apply to the
installation.
Standing Installation
If the unit is to be installed standing on a
surface, adjust the legs so that the unit stands
securely and is level (legs can be adjusted up
to 1”).
Do not install the unit standing directly on a
combustible surface. Use a 3” non-
combustible base.
Use the included L brackets to connect the unit
to a wall to ensure that it does not fall over.
These brackets will maintain the required 1”
clearance between the back of the unit and a
combustible surface.

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Combustion Air Supply
The water heater location must provide enough
air for proper combustion and ventilation of the
surrounding area. See the latest edition of
ANSI Standard Z223.1 or any applicable local
codes. In general, these requirements specify
that if the unit is installed in a confined space,
there must be a permanent air supply opening.
Air Supply from Outside Building
When combustion air is supplied from outside
the building, an opening communicating
directly with the outside should have a
minimum free area of one square inch per
15,000 BTUH input of the total input rating of
water heater in the enclosed area.
Air Supply from Inside Building
When combustion air is supplied from inside
the building, an opening communicating with
the rest of the dwelling should have a minimum
free area of one square inch per 1000 BTUH
input of the total input rating of water heater in
the enclosed area. These openings should
never be less than 100 sq. in.
Minimum recommended air supply opening size
for water heater:
Combustible Air Supplied by
Mechanical fan or Make up air device.
The T-K2 water heater is equipped with a
combustible air sensor that will shut off the unit
when inadequate combustible air supply to unit
is detected.
If a mechanical fan or make up air device is
used to supply air to the water heater or utility
room, the installer should make sure it does
not create drafts which could cause nuisance
shutdowns. If a blower is necessary to provide
adequate combustion air to the water heater, a
switch or equivalent device must be wired
(interlocked) with the water heater control
circuit or other proper devices to prevent the
water heater from firing unless the blower is
operating.
VENTING INSTRUCTIONS
General
WARNING: Improper venting of this appliance
can result in excessive levels of carbon
monoxide which can result in severe personal
injury or death.
This water heater must be vented in
accordance with the section “Venting of
Equipment" of the latest edition of the Natural
Fuel Gas Code, ANSI Z223.1 and all
applicable local building codes. In Canada,
follow section 7 of the CAN/CSA B149.1
Natural Gas and Propane Installation Code.
Exhaust Vent
This is a Category III appliance and must be
vented accordingly. The vent system must be
sealed air tight. All seams and joints must be
sealed with high heat resistant silicone sealant
or UL listed aluminum adhesive tape having a
minimum temperature rating of 350ºF. For best
results, a vent system should be as short and
straight as possible.
This unit requires 4”, Category III approved,
single wall stainless steel vent pipe or any
other Category III approved, non-combustible,
corrosion-resistant material. The following are
UL listed manufacturers: ProTech Systems Inc.
(FasNSeal), Flex-L Inc., Z-Flex Inc. (Z-Vent III)
and Heat-Fab Inc. (Saf-T Vent). Follow the
vent pipe manufacturer’s instructions when
installing the vent pipe. Do not common vent
this appliance with any other vented appliance.
The maximum length of exhaust vent piping
must not exceed 35 ft. deducting 5 ft. for each
elbow used in the venting system. Do not use
more than 3 elbows.
Diam
eter
Max.
No. of
Elbow
Max. Vertical or
Horizontal run in
Length
4” 3 Ea. 35 ft
For each elbow added, deduct 5 ft. from
max. Vent length.
No. of Elbows Max. Vertical or
Horizontal Length
0 35 ft.
1 30 ft.
2 25 ft.
3 20 ft.
Water heater
size
When drawing
make-up air
from outside
the building
When drawing make-up
air from inside the
building (from other
rooms within)
Max. 185,000
BTU
12.3 Sq. IN 185 Sq. IN

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When installing the vent system, all applicable
national and local codes must be followed. If
you install thimbles, fire stops or other
protective devices and they penetrate any
combustible or noncombustible construction,
be sure to follow all applicable national and
local codes.
When the horizontal vent run exceeds 5 ft., the
following criteria must be observed:
•Support the vent run at 3 ft intervals with
overhead hangers.
•Slope the vent run downwards toward the
vent terminator at a rate of ¼” per foot.
Vent Termination
A sidewall vent terminator must be used when
the water heater is vented through a sidewall.
Takagi recommends the use of its part No.TK-
TV01. The vent terminator provides a means of
installing vent pipe through the building wall
and must be located in accordance with ANSI
Z223.1/NFPA 54, or in Canada with CAN/CSA-
B149.1 and local applicable codes.
Locate the vent terminator so that it cannot be
blocked by snow. Most codes require that the
terminator be at least 12 inches above grade,
but the installer may determine if it should be
higher depending on the job site condition and
applicable codes.
WARNING: Improper installation can cause
nausea or asphyxiation, severe injury or death
from carbon monoxide and flue gases
poisoning. Improper installation will void
product warranty. For high altitude installation
above 4,500 feet, contact Takagi on how to
handle this situation.
General rules for venting the T-K2 water heater
are:
1. Place the water heater as close as possible
to the vent terminator;
2. The vent collar of the water heater must be
fastened directly to an unobstructed vent
pipe.
3. Do not weld the vent pipe to the water
heater collar.
4. The weight of the vent stack must not rest
on the water heater.
5. The vent must be easily removable from
the top of the water heater for normal
service and inspection of the unit.
6. The water heater vent must not be
connected to any other gas appliance or
vent stack.
7. Avoid locating the water heater vent
terminator near any air intake devices or
air-conditioning units. These fans can pick
up the exhaust flue products from the water
heater and return them to the building. This
can create a health hazard.
8. Avoid using an oversized vent pipe or using
extremely long runs of the pipe.

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Canada U.S.A
Direct vent and
other than Direct Vent Direct vent Other than Direct Vent
A Clearance above grade, veranda, porch,
deck, or balcony. 1 foot 1 foot 1 foot
B Clearance to window or door that may be
opened. 3 feet 1 foot
4 feet from below or
side opening. 1 foot
from above opening.
C Clearance to permanently closed window * * *
D
Vertical clearance to ventilated soffit located
above the vent terminator within a horizontal
distance of 2 feet (61cm) from the center
line of the terminator.
* * *
E Clearance to unventilated soffit * * *
F Clearance to outside corner * * *
G Clearance to inside corner * * *
H Clearance to each side of center line
extended above meter/regulator assembly 3 feet * *
I Clearance to service regulator vent outlet. 3 feet * *
J
Clearance to non-mechanical air supply inlet
to building or the combustion air inlet to any
other application.
3 feet 1 foot
4 feet from below or
side opening. 1 foot
from above opening.
K Clearance to mechanical air supply inlet. 6 feet 3 feet 3 feet
L Clearance above paved sidewalk or paved
driveway located on public property. 7 feet * 7 feet
M Clearance under veranda, porch deck, or
balcony. 1 foot * *
*For clearances not specified in ANSI Z223.1 / NFPA 54 or CAN/CSA-B149, please use clearances in accordance
with local installation codes and the requirement of the gas supplier.

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GAS SUPPLY AND GAS PIPE SIZING Check that the type of gas matches the rating
plate located on the cover of your water heater.
The minimum and maximum inlet gas pressures
are:
Natural Gas Min. 5” WC - Max. 10.5” WC
Propane Gas Min. 11” WC - Max. 14” WC
Gas pressure below this specified range for the
T-K2 and/or insufficient gas volume will adversely
affect performance. Inlet gas pressure must not
exceed the above maximum values; gas pressure
above the specified range will cause dangerous
operating conditions and damage to the unit. Until
testing of the main gas line supply pressure is
completed, ensure the gas line to the T-K2 is
disconnected to avoid any damage to the water
heater.
Size the gas pipe appropriately to supply the
necessary volume of gas required for the T-K2
(185,000 BTUH) using ANSI233.1/NAPA 54 in
the USA or CAN/CSA B149.1 in Canada or local
codes. Install a manual gas shut-off valve
between the T-K2 and the gas supply line.
When the gas connections are completed, it is
necessary to perform a gas leak test either by
applying soapy water to all gas fittings and
observing for bubbles or by using a gas leak
detection device. Always purge the gas line of
any debris before connecting to the heater gas
inlet.
Pipe Sizing Example: This table below is for
Natural gas piping supply straight to the water
heater without any tabs to other gas appliances
Recommend Gas pipe size for
T-K2 Water Heater (Example for NG)
Distance from Gas Meter Pipe Size (inches)
0' - 30' 3/4"
30' - 100' 1"
100' – 200’ 1-1/4"
TO TU
R
N OFF GAS TO
APP
LIAN
CE
1. Turn off all electric power to the water
heater if service is to be performed.
2. Turn the manual gas valve located on the
outside of the unit clockwise 3to the off
p
osition.
FOR YOUR SAFETY, READ
BEFORE OPERATING:
A. This water heater does not have a pilot. It
is equipped with an electronic ignition
device that automatically lights the burner.
Do not try to light the burner manually;
B. BEFORE OPERATING, check all around
the water heater area for gas leaks. Be
sure to check next to the floor as some
gases are heavier than air and will settle
on the floor;
C. Use only your hand to turn the gas valve
knob. Never use tools. If the knob will not
turn by hand, do not attempt to repair it.
Call a qualified service technician. Force
or attempted repair may result in a fire or
explosion.
D. WARNING: Conversion of this unit from
natural gas to propane or propane to
natural gas cannot be done in the field.
Contact your local distributor to get the
correct unit for your gas type. Conversion
done by anyone other than the
m
a
n
u
f
ac
t
u
r
e
r will v
o
i
d
a
ll w
a
rr
a
nt
y
.

- 11 -
Natural Gas Supply Piping
Maximum Capacity of Natural Gas Based on a 0.60 specific gravity at a 0.5” WC pressure drop
Pipe Size kBTU of Natural Gas
Length 10’ 20’ 30’ 40’ 50’ 60’ 70’ 80’ 90’ 100’ 125’ 150’ 200’
¾” 372 255 205 175 156 142 130 121 114 107 95 86 74
1” 702 482 387 331 293 266 245 228 213 202 179 162 139
1 ¼” 1441 990 795 680 603 546 503 468 439 415 367 332 285
1 ½” 2158 1483 1191 1019 903 819 753 701 658 621 550 499 427
2” 4155 2856 2293 1963 1740 1576 1450 1349 1266 1195 1060 960 822
Propane (LP) Gas Supply Piping
Maximum Capacity of Propane (LP) Gas Based on 11” WC supply pressure at a 1.0” WC pressure drop
Pipe Size kBTU of Propane
Length 10’ 20’ 30’ 40’ 50’ 60’ 70’ 80’ 90’ 100’ 125’ 150’ 200’
¾” 567 393 315 267 237 217 196 185 173 162 146 132 112
1” 1071 732 590 504 448 409 378 346 322 307 275 252 213
1 ¼” 2205 1496 1212 1039 913 834 771 724 677 630 567 511 440
1 ½” 3307 2299 1858 1559 1417 1275 1181 1086 1023 976 866 787 675
2” 6221 4331 3465 2992 2646 2394 2205 2047 1921 1811 1606 1496 1260
WATER CONNECTIONS
All pipes, pipe fittings, valves and other
components, including soldering materials,
must be suitable for potable water systems. A
manual shut off valve must be installed on the
cold water inlet to the water heater between
the main water supply line and the T-K2. In
addition, a manual shut off valve is also
recommended on the hot water outlet of the
unit. If the T-K2 is installed within, or subjected
to, a closed loop water system, such as one
having an anti-backflow device in the cold
water supply line, a thermal expansion tank
must be installed. Contact the water supplier or
local plumbing inspector on how to control this
situation.
After installation of the water heater is
complete, purge the water line to remove all
the debris and air from the line. Failure to do
so may cause damage to the heater. There is
a wire mesh filter within the cold inlet to trap
debris from entering your heater. This will need
to be cleaned periodically to maintain optimum
flow.
Unit Draining & Filter Cleaning Procedures
To drain your unit, please follow these
instructions carefully:
1. Turn off the power supply to the T-K2
Water Heater.
2. Close the manual gas shut off valve
located on the gas supply line.
3. Close the manual water shut off valve
located on the water supply line.
4. Open all hot water taps in the house.
(Bathroom, kitchen, laundry room, etc.).
When the residual water flow has ceased,
close all hot water taps.
5. Have a bucket or pan to catch the water
from the unit’s drain plugs. Remove the
drain plugs to drain all the water out of the
unit.
6. Wait a few minutes to ensure all water has
drained from unit.
7. At this time, please check the water filter
located within the cold inlet. With a tiny
brush, clean the water filter of any debris
which may have accumulated and reinsert
the filter back into the cold water inlet.
8. Securely screw the drain plugs back into
place. Hand- tighten only
FOR YOUR SAFETY, READ
BEFORE OPERATING:
Do not use this water heater if any part
has been submersed under water.
Immediately call a qualified service
technician to inspect the water heater and
to replace any damaged parts.

- 12 -
To re-start your heater, follow these steps:
1. Make sure all hot water taps are closed
and the drain plugs are securely attached.
2. Purge the water line of debris.
3. Open the manual water shut-off valve
located on the water supply line.
4. Open all the hot water taps to verify water
flows to the taps. Then close the hot water
taps.
5. Open the manual gas shut-off valve located
on the gas supply line.
6. Turn on the power supply to the T-K2
Water Heater.
Note: Do not reverse the hot outlet and cold
inlet connections to the T-K2 Water Heater.
This will not activate the water heater.
Pressure Relief Valve
The FLASH T-K2 has a high-temperature shut
off switch built in as a standard safety feature
(called a Hi-Limit switch) therefore a “pressure
only” relief valve is required.
This unit does not come with an approved
pressure relief valve. An approved pressure
relief valve must be installed on the hot water
outlet. The pressure relief valve must conform
to ANSI Z21.22 or CAN 1-4.4 and installation
must follow local code.
The discharge capacity must be at least
185,000 BTU/hr. The discharge piping for the
pressure relief valve must be directed so that
the hot water cannot splash on anyone or on
nearby equipment. Attach the discharge tube
to the pressure relief valve and run the end of
the tube to within 6" from the floor. This
discharge tube must allow free and complete
drainage without any restrictions.
If the pressure relief valve installed on the T-K2
discharges periodically, this may be due to a
defective thermal expansion tank or defective
pressure relief valve.
The pressure relief valve must be manually
operated periodically to check for correct
operation.
ELECTRICAL CONNECTIONS
WARNING: Follow the electrical code
requirements of the local authority having
jurisdiction. In the absence of such
requirements, follow the latest edition of the
National Electrical Code ANSI/NFPA 70 in the
U.S. or the latest edition of CSA C22.1
Canadian Electrical Code, Part 1, in Canada.
The heater must be electrically grounded. Do
not attach the ground wire to either the gas or
the water piping. Plastic pipe or dielectric
unions may isolate the water heater
electrically.
CAUTION: When servicing or replacing parts
within the T-K2, label all wires prior to
disconnection to facilitate an easy and error
free reconnection. Wiring errors can cause
improper and dangerous operation. Verify
proper operation after servicing.
The FLASH T-K2 water heater requires AC
120V 60 Hz electrical power supply that is
properly grounded.
•An on/off switch controlling the main power
to the T-K2 must be provided for service
reasons;
•Connect the power supply to the T-K2
exactly as shown in the wiring diagram;
A green screw is provided in the junction box
to ground the connection.

- 13 -
Wiring diagrams are also located on the
inside panel of the appliance.

- 14 -
INITIAL OPERATION
For your safety please read before
operating the unit for the first time.
Once you have properly installed the unit and
before firing it for the first time, check the gas
and water connections for leaks. Open the
main gas supply valve to the unit using only
your hand to avoid any spark. Never use tools.
If the knob will not turn by hand, do not try to
force it; call a qualified service technician.
Force or attempted repair may result in a fire or
explosion due to gas leaks. Be sure to check
next to the bottom of the unit because some
gases are heavier than air and may settle
towards the floor.
CAUTION: IF YOU SMELL GAS:
1. Do not try to start the water heater.
2. Do not touch any electric switch; do not
use any phone in your building.
3. Immediately call your gas supplier from
a neighbor’s phone. Follow the gas
supplier’s instructions.
4. If you cannot reach your gas supplier,
call the fire department.
This water heater does not have a pilot light. It
is equipped with an electronic ignition device
which automatically lights the burner. Do not
try to light the burner manually. Check for
proper venting and combustible air to the
heater. Purge the gas and water lines to
remove any air pocket. Do not use this water
heater if any part has been submersed under
water. Immediately call a qualified service
technician to inspect the water heater and to
replace any parts that have been under water.
Once the above checks have been completed,
follow these steps to turn on your unit:
1. Close the manual gas control valve located
on the gas line.
2. Fully open the manual water control valve
on the water supply line.
3. Open a hot water tap to verify that water is
flowing to that tap. Then close the hot
water tap.
4. Fully open the manual gas control valve
installed.
5. Turn on the 120 volt 60 Hz power supply to
the FLASH T-K2 water heater.
6. Now you are ready to enjoy hours of
endless hot water.
NORMAL OPERATION
To Turn on Your FLASH T-K2 water heater.
1. Open a hot water tap.
2. Burners ignite. “Fire On” lamp is lit.
3. Mix cold water with the hot to get the
correct temperature water.
To "Turn off your Mobius water heater
1. Close the hot water tap
“Fire On” lamp extinguishes.
FLOW
The flow rate through the FLASH T-K2 is
limited to a maximum of 6.9 GPM. The
temperature setting, along with the supply
temperature of the water will determine the
flow rate output of the unit. Please refer to the
temperature/gallons per minute chart at the
back of this manual to determine the likely flow
rates based on your local ground water
temperature and your desired outlet water
temperature combination.
Based on the United States Department of
Energy method of testing water heater output,
the T-K2 is rated for 228 gallons per hour
(GPH), or 3.8 gallons per minute (GPM), when
raising the water temperature by 77°F (for
example from 43°F to 120°F). Refer to the
following chart of typical household plumbing
fixture flow rates to determine what the FLASH
T-K2 can do in a household application.

- 15 -
TEMPERATURE SETTINGS
There are 4 preset temperatures that you can
select from by adjusting the dipswitch settings
on the computer board. The temperature has
been preset at the factory to122ºF (50ºC). The
computer will electronically control this
temperature. At a fixture, mix cold water with
hot to get the water temperature you desire. If
you desire a hot water temperature other than
the 4 preset settings, please purchase the
optional temperature remote controller (part
No. TK-RE02). With this optional TK-RE02 you
can set the temperature from 99ºF to 176ºF.
Please carefully read the instructions prior to
installing the TK-RE02 as failure to do so could
damage the temperature controller and/or the
water heater, which will void the warranty.
Hot Water Output Temperature Setting:
With the FLASH T-K2 Water Heater, the output
hot water temperature can be adjusted either
manually from the main computer board’s
dipswitches or with the optional remote
controller (Part TK-RE02, from 99°F to 176°F).
The dipswitches can set four hot water output
temperatures 104°F, 113°F, 122°F, and 176°F
(the factory set temperature is 122°F). could
damage the temperature controller and/or the
water heater, which will void the warranty.
FREEZE PROCTECTION DEVICES
This unit comes equipped with heating blocks
to prevent freezing which can damage the heat
exchanger. For this freeze prevention system
to operate, there has to be electrical power to
the unit. Damage to the heat exchanger
caused by freezing temperatures due to power
loss is not covered under the warranty.
The unit has been rated for temperatures down
to 5ºF (-15ºC) in a wind free environment. If
you install the water heater in an area that is
subject to temperatures (including wind chill)
below 5ºF (-15ºC), this will void the warranty
and Takagi will not be responsible for any
damage to the heat exchanger as a result of
freezing. In any areas subject to freezing
temperatures, Takagi strongly recommends
the use of its back flow prevention flue damper
(Part No. TK-TV03) to reduce the amount of
cold air entering through the exhaust venting
when the water heater is off.
If you will not be using your heater for a long
period of time or if the temperatures (including
the wind chill) will drop below 5 ºF (-15 ºC),
turn off your heater and drain the unit of water
Household Flow Rates
Appliance / Use Flow Rate
(GPM)
Lavatory Faucet 1.0
Bath Tub 4.0
Shower 2.0
Kitchen Sink 1.5
Dishwasher 1.5
Washing Machine 2.0
Taken from UPC 1997
WARNING
Hot Water Heater temperatures over
125°F can cause severe burns instantly or
death from scalding. The outlet hot water
temperature of the FLASH T-K2 water
heater is factory set at 122°F. Feel the
water temperature before bathing or
showering. Do not leave children, the
disabled or the elderly unattended as they
are at the highest risk of being scalded.
Temperature limiting valves are available,
ask professional person.

- 16 -
(see ‘Unit Draining & Filter Cleaning’ section
above for draining instructions). This will keep
your unit from freezing and being damaged.
For indoor installation in areas where the
temperature will be well below freezing for
extended periods of time, use the “thermostat
extension cable” to relocate the internal
thermostat located on the fan motor to the
outdoors. This will sense the ambient air
temperature and turn the internal heater blocks
on to help prevent the heat exchanger from
freezing.
The thermostat is attached to the motor fan.
The computer may need to be removed to gain
access to the thermostat. Remove the
thermostat from the fan and extend the cable
to locate the thermostat outdoors where it can
get a better ambient temperature reading.
CAUTION: Only the pipes within the water
heater are protected by the anti-freeze devices
on the T-K2. Any hot or cold water pipes
located outside of the unit will not be protected.
Properly protect and insulate these pipes from
freezing.
CAUTION: Label all wires prior to
disconnection when servicing controls. Wiring
error can cause improper and dangerous
operation. Verify proper operation after
servicing.
The FLASH T-K2 water heater requires an
electrical power supply from 120 VAC 60 Hz
circuit and be properly grounded.
•A means for switching on/off the 120 VAC
power supply must be provided for service
reasons.
•Wire the heater exactly as shown in the
wiring diagram.
•A green screw is provided in the junction
box for grounding connection.
MAINTENANCE AND SERVICE
WARNING: Turn off the electrical power
supply and close the manual gas control
valve and the manual water control valve
before servicing.
Do this immediately after installation.
1. Clean the cold-water inlet filter (figure
below).
2. Be sure that all openings for combustion
and ventilation air are not blocked.
3. Check that the exhaust vent pipe is not
blocked.
4. Check the gas pressure.
5. Keep the area around the water heater
clear. Remove any combustible materials,
gasoline or any flammable vapors and
liquids.
The unit should be checked once a year or as
necessary by a licensed technician. If repairs
are needed, any repairs should be done by a
licensed technician.
The following systems and parts should be
checked at least once a year:
1. Venting system
2. Burner
3. Manual operation of the pressure relief
valve to ensure correct operation.
4. Periodic cleaning of the water filter (figure
above).
5. Heat exchanger. Remove the thermistor
and check for a mineral coating. A mineral
coating on the thermistor requires flushing
the heat exchanger with a de-scaling
solution. Scale build up will void your
warranty and shorten the life of your water
heater.
Filter
OPEN
CLOSE

- 17 -
Common Trouble Shooting
The T-K2 can burn gas at a maximum input
rate of 185,000 BTUH. This puts a limit on the
possible output temperature and flow
capabilities. If the water doesn’t seem hot
enough, compare the flow and temperature
that is being attained to the T-K2 flow vs.
temperature chart (See flow chart on the last
page of this manual). If the unit is not
performing according to the chart, first check
that the gas supply pipe is sized properly and
that the gas pressure is within the required
range. If the gas line is sized properly, check
the plumbing for mixing valves, thermostatic
valves, anti-scald devices, single handled
faucets with built in temperature or pressure
compensators valves and hot and cold crossed
connections. If the unit is performing in
accordance with the flow chart, it may be
undersized for the application. If the unit is
performing according to the chart, the output
temperature can be adjusted using the TK-
RE02 or the dipswitches on the unit.
It Takes Too Long to Get Hot Water
The T-K2 takes three seconds to ignite and
three more seconds to heat the incoming
ground water up to the set temperature. The
time it takes to deliver hot water from the T-K2
to your fixtures depends on the length of piping
between the two. The longer the distance, the
more time it will take. If you would like to
receive hot water to your fixtures quicker, you
may want to consider a hot water recirculation
system.
The T-K2 Will Not Initiate
First check the flow rate through the unit. If the
flow is less than .75 GPM, the unit will not
initiate. Check the filter for any debris or
damage. If you have installed a combination
system (a T-K2 doing both domestic hot water
and space heating), completely isolate the
heating system temporarily to ensure flow is
not backfeeding through your heating system
to supply the domestic water (by-passing the
T-K2).
If neither of those remedies start the unit, press
the lower grey button marked “test (off)” on the
GFCI inside the unit. If the red light above it
does not come on, there is a problem with the
electrical supply to the unit. If that red light
does come on, hit the “reset (on)” button and
open a hot water faucet to re-try the unit. If the
problem persists contact Takagi for instructions
ERROR CODES
All Takagi units are self diagnostic for safety
and convenience when trouble shooting. If
there is a problem with the installation or the
unit, it will display a numerical error code on
the TK-RE02 (if installed) or at the bottom left
corner of the computer board to communicate
the source of the problem. Consult the
following chart for the cause of an error code:
The T-K2 consists of five major control
operations: Temperature control, Gas control,
Water control, Burner Control, and Main
computer control.
Computer Board TK-RE02 Check Point
11 Igniter
12 Flame Detector
51 Main Gas Valve
Burning (red) LED: Blinking
Power (green) LED: OFF
72 Pre Post Check
03 Wrong Gas, Dip Switch
14 Hi-Limit Switch
70 Computer Board
Burning (red) LED: OFF
Power (green) LED: Blinking
71 Proportional Valve
61 Fan MotorBurning LED and Power LED:
Blinking Alternately 21 Vent Pipe
31 ThermistorBurning LED and Power LED:
Blink Simultaneously 65 Water Control Valve

17
Wiring Diagram
A wiring diagram is located on the inside front panel of the appliance.
Electrical Rating: 120 VAC, 60 Hz, 0.8 A.
Note: If any of the original wiring supplied with this appliance must be replaced, it must be replaced with
appliance wiring material (180c) or its equivalent. Replacement wires are available through Takagi.

18
OPERATING INSTRUCTIONS
1. STOP! Read the safety information above or in the Owners Manual.
2. Turn off all electric power to the water heater.
3. Do not attempt to light the burner by hand.
4. Turn the gas manual gas valve located on the outside of the unit clockwise ↻to the
off position.
5. Wait five (5) minutes to clear out any gas. If you then smell gas. STOP! Follow "B"
in the safety information above on this label. If you don't smell gas, go to next step.
6. Turn the manual gas valve located on the outside of the unit counter clockwise ↺
to the ON position.
7. Turn on all electrical power to the water heater.
8. If the water heater will not operate, follow the instructions “to Turn Off Gas to water
heater" and Call your service technician or gas supplier.
FOR YOUR SAFETY READ BEFORE OPERATING
WARNING: If you do not follow these instructions exactly, a fire or
explosion may result causing property damage, personal injury or loss of
life.
A. This water heater does not have a pilot. It is equipped with an ignition device that
automatically lights the burner. Do not try to light the burner by hand.
B. BEFORE OPERATING smell all around the water heater area for evidence of
leaking gas. Be sure to smell next to the floor because some gas is heavier than air
and will settle on the floor.
WHAT TO DO IF YOU SMELL GAS.
•Do not try to light any appliance.
•Do not touch any electric switch, do not use any phone in your building
•Immediately call your gas supplier from a neighbor's phone. Follow the gas
supplier's instructions.
•If you cannot reach your gas supplier, call the fire department.
C. Use only your hand to turn the gas valve knob. Never use tools. If the knob will not
turn by hand, don't try to repair it. Call a qualified service technician. Force or
attempted repair may result in a fire of explosion.
D. Do not use this water heater if any part has been under water. Immediately call a
qualified service technician to inspect the water heater and to replace any damaged
parts.
TO TURN OFF GAS TO APPLIANCE
1. Turn off all electric power to the water heater if service is to be performed.
2. Turn the manual gas valve located on the outside of the unit clockwise ↻to the off
position.

19
Vapors from flammable liquids will explode and catch fire causing death or severe burns.
Do not use or store flammable products such as gasoline, solvents or adhesives in the
same room or area near the water heater.
WARNING: Do not install water heater where flammable products will be stored.
Read and follow water heater warnings and instructions. If owner's manual is
missing, contact the retailer or manufacturer.
W
ARNING
The outlet hot water temperature of the T-K2 water heater is factory set at 122 °F.
WARNING: Use this heater at your own risk. The set outlet water temperature can cause
severe burns instantl
y
or death from scalds. Test the water before bathin
g
or showerin
g
.
DANGER
Hot Water Heater temperature over 125 °F can cause
severe burns instantly or death from scalding.
Children, disabled and elderly are at the highest risk of
being scalded. Feel water temperature before bathing or
showering. Temperature limiting valves are available, ask
p
rofessional
p
erson.
DANGER
Keep flammable products:
1. Far away from heater.
2. In approved containers.
3. Tightly closed
4. Out of children's reach
Vapors:
1. Cannot be seen
2. Vapors are heavier than air
3. Go a long way on the floor
4. Can be carried from other rooms
to the main burner b
y
air currents.
WARNING: California Proposition 65 lists chemical substances known to the state to
cause cancer, birth defects, death, serious illness or other reproductive harm. This product
may contain such substances, be their origin from fuel combustion (gas, oil) or
components of the product itself.