Bosch 125HX User manual

6 720 606 804 US (04.11) AL
WARNING: Improper installation,
adjustment, alteration, service or maintenance can cause
injury or property damage. Refer to this manual. For
assistance or additional information consult a ualified
installer, service agency or the gas supplier.
Upon completion of the installation, these instructions
should be handed to the user of the appliance for future
reference.
In the Commonwealth of Massachusetts this product
must be installed by a licensed plumber or gas fitter.
INSTALLATION AND OPERATING INSTRUCTIONS FOR AUTOMATIC
INSTANTANEOUS TYPE WATER HEATERS FOR USE WITH NATURAL AND
LIQUEFIED PETROLEUM GAS
MODEL 125HX LP and 125HX NG
(Flow Modulated with Electronic Ignition)
Suitable for heating potable water only
Not approved for space heating purposes
Intended for variable flow applications with steady cold water inlet temperatures.
WARNING
If the information in this manual is not followed exactly, a
fire or explosion may result causing property damage,
personal injury or death.
FOR YOUR SAFETY
Do not store or use gasoline or other flammable,
combustible or corrosive vapors and li uids in the vicinity
of this or any other appliance.
WHAT TO DO IF YOU SMELL GAS
-Do not try to light any appliance.
-Do not touch any electrical 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.
-Installation and service must be performed by a
ualified installer, service agency or the gas supplier.
TABLE OF CONTENTS
Specifications .............................................................................Page 3
Ru es for safe operation ........................................................... Page 5
Locating the Heater .................................................................. Page 5
Combustion Air Requirements ...............................................Page 6
Mounting the Heater................................................................. Page 6
Venting the Heater.....................................................................Page 7
Gas Connections ...................................................................... Page 9
Gas Piping ................................................................................Page 10
Water Connections .................................................................Page 11
Safety before turning on the heater .....................................Page 11
Operating instructions ...........................................................Page 12
Setting water temperature ....................................................Page 12
Maintenance & Service ...........................................................Page 13
Troub e Shooting .....................................................................Page 13
E ectrica Diagram ....................................................................Page 15
Diagram of 125HX .................................................................. Page 17
Interior components diagram ...............................................Page 18
Parts List ...................................................................................Page 19
F owchart ................................................................................. Page 20
Warranty ....................................................................................Page 21

26 720 606 804
WARNING: Improper installation,
adjustment, alteration, service or maintenance can cause
injury or property damage. Refer to this manual. For
assistance or additional information consult a ualified
installer, service agency or the gas supplier.
Upon completion of the installation, these instructions
should be handed to the user of the appliance for future
reference.
In the Commonwealth of Massachusetts this product
must be installed by a licensed plumber or gas fitter.
WARNING
If the information in this manual is not followed exactly, a
fire or explosion may result causing property damage,
personal injury or death.
FOR YOUR SAFETY
Do not store or use gasoline or other flammable,
combustible or corrosive vapors and li uids in the vicinity
of this or any other appliance.
WHAT TO DO IF YOU SMELL GAS
-Do not try to light any appliance.
-Do not touch any electrical 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.
-Installation and service must be performed by a
ualified installer, service agency or the gas supplier.

36 720 606 804
Principle of Operation:
When a hot water faucet is opened, the water f ow through
the heater causes the gas va ve to open. At the same time
the hydro-generator activates the e ectronics which sends
a spark to the pi ot. The f ame sensor confirms the pi ot has
been ighted and a ows the first two burners to come on.
The f ame sensor confirms correct activation and a burners
come on. The pi ot goes off. The heat exchanger coi s absorb
the heat generated by the burners and transfer heat to the
water. When the hot water faucet is shut off, the gas va ve
automatica y c oses and the burners turn off. Your hot water
faucet is an ignition key to activate the water heater, giving
you contro over your hot water energy use. Every time you
turn off your hot water faucet, the energy consumption of
your hot water returns to zero.
FEATURES
- E ectronic Pi ot Ignition driven by hydro-generator
- High Qua ity Materia s for Long Working Life.
- Copper heating coi s for end ess supp y of hot water.
- Burner output proportiona to hot water f ow demand for
maximum energy efficiency.
- Safety f ame sensor at pi ot burner.
- Automatic overheating protection shut-off sensor.
- F ue gas safety device.
- Stain ess stee burners with stabi ized b ue f ame.
- Bui t-in corrosion resistant draft diverter.
- Compact space saver: mounts on a wa with two hooks.
- Easi y removab e one-piece cover.
- Easy one person insta ation.
- Adjustab e water f ow restrictor to ensure that water f ow
demand wi not exceed the heating capacity of the heater.
- On/Off Switch to activate system.
- Red LED indicator f ashes with ow water pressure.
- Green LED indicator main burner operation.
BOSCH is constant y improving our products, therefore
specifications are subject to change without prior notice.
125 HX LP and 125 HX NG Specifications
Gas Input max.: 117,000 Btu/hr
min.: 28,000 Btu/hr
Water Connection ½” Thread fitting NPT
H x W x D 29 3/4” x 18 1/4” x 8 3/4"
Vent 5”
Gas Connection 1/2” NPT thread
Min. Water Pressure 18 Psi at 4 GPM
Max. Water Pressure 150 Psi
Shipping Weight 43 LB
Net Weight 40 LB
1.8 GPM at 90° rise
3.7 GPM at 45° rise
Min. Water F ow 1/2 ga /min
LP GAS Supp y Pressure
(before 125 HX regu ator) min. 11” W.C.
max. 14” W.C.*
Required LP GAS Pressure at in et
tap whi e 125 HX is operating: 10.5” W.C.
LP GAS Burner Manifo d pressure whi e 125 HX is
operating at maximum input: 9.0” W.C.
Natura Gas Supp y Pressure min.: 7” W.C.
(before 125 HX regu ator) max.: 14” W.C.*
Required Natura Gas Pressure at in et
tap whi e 125 HX is operating: 5.7” W.C.
Natura Gas Burner Manifo d Pressure whi e 125 HX is
operating at maximum input: 4.2” W.C.
* In et gas pressure before 125 HX regu ator must not exceed
this va ue. Pressure may need to be adjusted for high
a titudes, see page 9.
UNPACKING THE 125 HX HEATER
This heater is packed secure y. The box inc udes one water connection fitting, a contro knob with co ar, a gas pressure
regu ator, a pressure re ief va ve, an incandescent partic e tray, two hooks for hanging the heater, this manua and a
warranty registration card. Do not lose this manual, as there is a charge for replacement. P ease comp ete and return
the enc osed warranty registration card.

46 720 606 804
MINIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON
COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS
FRONT VIEW SIDE VIEW
MODEL 125HX
MODEL 125 HX
TOP (A) 12"
FRONT (B) 4"
BACK 0"
SIDES 4"
FLOOR (C) 12"
VENT DIAMETER 5"

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GENERAL RULES TO FOLLOW
FOR SAFE OPERATION
1. You shou d fo ow these instructions when you insta your
heater. In the United States: The insta ation must conform
with oca codes or, in the absence of oca codes, the
Nationa Fue Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Insta ation shou d conform with CGA
B149.(1,2) INSTALLATION CODES and /or oca insta ation
codes.
2. Carefu y p an where you insta the heater. Correct
combustion air supp y and f ue pipe insta ation are very
important. If not insta ed correct y, fata accidents can be
caused by ack of air, carbon monoxide poisoning or fire.
3. The p ace where you insta the heater must have enough
venti ation. The Nationa Fire Codes do not a ow gas fired
water heater insta ation in bathrooms, bedrooms or any
occupied rooms norma y kept c osed. See the section be ow
on ocating the heater.
4. You must vent your heater. See section on VENTING,
Page 7.
5. The app iance must be disconnected from the gas supp y
piping system during any pressure testing at pressures in
excess of 1/2 Psig (3.5 kPa).
The app iance must be iso ated from the gas supp y piping
system by c osing its individua manua shutoff va ve during
any pressure testing of the gas supp y piping system at test
pressures equa to or more than 1/2 Psig (3.5Kpa). The
app iance and its gas connection must be eak tested before
p acing the app iance in operation.
6. Keep water heater area c ear and free from combustib es
and f ammab e iquids. Do not ocate the heater over any
materia which might burn.
7. Correct gas pressure is critica for the optimum
operation of this heater (see specifications on page 2). Gas
piping must be sized to provide the required pressure at the
maximum output of the heater, whi e a the other gas
app iances are in operation. Check with your oca gas
supp ier, and see the section on connecting the gas supp y.
8. Shou d overheating occur or the gas supp y fai to shut
off, turn off the gas supp y at the manua gas shut off va ve
on the gas ine.
9. Do not use this app iance if any part has been underwater.
Immediate y ca a qua ified service technician to inspect
the app iance and to rep ace any part of the contro system
and any gas contro which has been underwater.
PROPER LOCATION FOR INSTALLING YOUR
HEATER
Carefu y se ect the ocation of your new heater. For your
safety and for proper heater operation, you must provide an
abundant supp y of combustion air and a proper venting. Fig. 1 - Water heater drain plug
The heater may sti operate even when improper y vented.
It wi , however, be ess efficient and cou d eventua y damage
the heater. It cou d even resu t in human sickness or death
due to oxygen deprivation and carbon monoxide poisoning.
Fo ow the guide ines be ow:
1. P ace your heater as c ose to a vent or chimney as
possib e.
2. Nationa bui ding codes require that you do not insta
this app iance in bathrooms, bedrooms or any occupied
rooms norma y kept c osed.
3. Simu taneous operation of other app iances such as
exhaust fans, venti ation systems c othes dryers, firep aces
or wood stoves cou d create a vacuum effect in your home
which cou d cause dangerous combustion by-products to
spi back into your home rather than venting to the outside
through the f ue. Confirm that your 125 HX is venting
proper y when a these other app iances are running. See
section on venting.
Do not obstruct the flow of combustion and ventilation
air to the appliance. If insta ed near a c othes dryer it is
very important that the dryer be proper y vented. Fai ure to
proper y vent a dryer cou d resu t in a gradua accumu ation
of int on the water heater fin coi s and burners, eading to a
dangerous condition of vent b ockage and poor unsafe
combustion.
4. Your hot water ines shou d be kept short to save energy.
It is a ways best to have hot water ines insu ated.
5. This product is neither designed nor approved for outside
insta ations. This product is not approved for manufactured
homes (mobi e home), recreationa vehic es (RV) or boats.
Reference ANSI Z21.10.3.
WARNING: The water in this water heater is co d and
a ways remains co d except for the times that hot water is
being used DO NOT INSTALL IN AN AREA WHERE IT
COULD FREEZE.
This heater is neither designed for nor approved for
outside installation.
Drain the heater entirely if freezing temperatures are
anticipated in area where heater is installed by
disconnecting both the inlet and outlet water connections
from the heater (disconnect the outlet flex line from where
it connects to the copper heat exchanger). Additionally
remove the drain plug under the water valve. See Fig. 1.

66 720 606 804
WARNING: Flammable materials, gasoline,
pressurized containers, or any other items or articles
that are potentially fire hazards must NOT be placed on
or adjacent to the heater. The appliance area must be
kept free of all combustible materials, gasoline and other
flammable vapors and li uids.
COMBUSTION AIR REQUIREMENTS
The 125 HX water heater ho ds co d water in its copper
heat exchanger and brass water va ve when not in use.
Because of this, any co d air that comes down through the
unit’s vent pipe is capab e of freezing these components.
This Insta ation Manua specifies the minimum vertica vent
pipe and the amount of combustion air required for this unit.
When a requirements are fo owed, the unit wi operate
proper y and safe y. However, there may sti be a risk of
freezing due to negative draft if a the combustion app iances
in the area are not being supp ied with a sufficient amount
of make-up air. A wood stove or furnace may pu combustib e
air down through the 125 HX vent system, eaving the co d
infi trating air capab e of freezing the co d water in the 125
HX heat exchanger. More make up air is the so ution. Fo ow
the instructions on venting and checking adequacy of make
up air. A HVAC specia ist shou d be used to design so utions
for providing more make-up air if necessary.
Observe the fo owing instructions concerning combustion
air.
App iances ocated in unconfined spaces:
a) An unconfined space is one whose vo ume is greater
than 50 cubic feet per 1000 Btu per hour of the combined
rating of a app iances insta ed in the space. That wou d
be 5850 cubic feet for the AquaStar 125HX a one.
b) In unconfined spaces in bui dings of conventiona frame,
masonry, or meta construction, infi tration is norma y
adequate to provide air for combustion, venti ation, and
di ution of f ue gasses.
App iances ocated in confined spaces:
The confined space must be provided with two permanent
openings, one commencing within 12 inches of the top and
one commencing within 12 inches of the bottom of the
enc osure. Each opening must have a minimum free area of
one square inch per:
- 1000 Btu/hr if a air is taken from inside the bui ding.
- 2000 Btu/hr if a air is taken from the outside by horizonta
ducts.
- 4000 Btu/hr if a air is taken from the outside by direct
openings or vertica ducts.
Or the confined space must be provided with one permanent
opening or duct that is within 12 inches of the cei ing of the
enc osure. This opening must have a minimum free area of
one square inch per:
- 3000 Btu/hr if a air is taken from the outside by a direct
opening or vertica duct.
Louvers, gri s and screens have a b ocking effect. If the
effective free area is not known, increase the sizes of your
openings by 75% if your ouvers are wood and by 30% if
your ouvers are meta . Refer to the Nationa Fue Gas Code
for comp ete information. In bui dings of tight construction
a air shou d be taken from outside.
CLEARANCES
The 125 HX is design certified for insta ation on a
combustib e wa and for insta ation in an a cove or c oset
with the minimum c earances to combustib e and non -
combustib e construction isted be ow
A. Top 12 inches (306 mm)
B. Front 4 inches (102 mm)
C. Back 0 inches
D. Sides 4 inches (102mm)
E. Bottom 12 inches (306 mm)
C earance from vent is dependent upon the c earance rating
of the venting materia used. For examp e: type B-1 vent is
approved for 1 inch c earance.
Note: Typica y, the minimum c earence to combustib e
materia s shou d not be ess than 6“ for sing e wa f ue
pipe. Note that this c earance can be reduced if combustib e
materia s are protected as per tab e VI of the Nationa Fue
Gas Code or if Type B gas vent is used.
MOUNTING INSTALLATION
The 125HX is design certified for mounting on a wa .
Secure the two L shaped hooks, which are provided with
heater, to a wa surface. P ace them 13 ¼” apart as shown
in Fig. 2.
Do not insta this app iance on a carpeted wa or over f oor
covering which is combustib e, such as carpet. The heater
must be mounted on a wa using appropriate anchoring
materia s. If wa is a stud wa sheathed with p asterboard, it
is recommended that support board(s), either 1x4’s or
1/2" (minimum) plywood first be attached across a pair
of studs and then the heater should be attached to the
support boards. See Fig. 2.
Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted direct y to a britt e, friab e board, such as
125HX Air Vents
(5 ½ X 5 ½ in. each)
Air Vents
(10 ¾ X 10 ¾ in. each) 125HX

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VENTING
Vent pipe connection.
WARNING: Do not reduce the vent pipe size. See Fig. 4
for high altitude installations
The heater must be vented to the outside fo owing a oca
ordinances and specifications for insta ing a gas app iance
vent or chimney. The heater must be ocated as c ose as
practicab e to a vertica y rising chimney or vent that has a
isted vent cap at its termination point. The venting system
must be designed and constructed so as to deve op a posi-
tive f ow adequate to remove f ue gasses to the outdoors.
Consult the National Fuel Gas Code if the vent will have
elbows or share venting with another natural draft
Roof pitch H (minimum) feet meters
Flat to 6/12 1.0 0.30
6/12 to 7/12 1.25 0.38
Over 7/12 to 8/12 1.5 0.46
Over 8/12 to 9/12 2.0 0.61
Over 9/12 to 10/12 2.5 0.76
Over 10/12 to 11/12 3.25 0.99
Over 11/12 to 12/12 4.0 1.22
Over 12/12 to 14/12 5.0 1.52
Over 14/12 to 16/12 6.0 1.83
Over 16/12 to 18/12 7.0 2.13
Over 18/12 to 20/12 7.5 2.27
Over 20/12 to 21/12 8.0 2.44
GAS VENT TERMINATIONS FOR LISTED VENT CAPS
Listed vent cap
Lowest discharge
opening
H (minimum) height
from roof to owest
discharge opening
Roof Pitch
IS X/12
12
X
Listed gas vent
Figure A Figure B
Establish a one foot
rise before any elbows
MINIMUM 6 FEET (1.8M)
Listed vent cap
p asterboard, can cause fai ure of mounting.
In earthquake-prone zones, CEC recommends that insta ers
use a arge washer and ag screw through the existing ho es
used to hang the heater to affix the upper third of the heater
to the mounting board. To affix the ower third of the heater,
CEC recommends that two new ho es be dri ed in the
heater’s frame, each one 16 inches be ow the top two ho es,
and that washers and ag screws be used to secure the
ower portion of the heater to a spacing board.
Before installing the unit, be certain you have the correct
heater for your type of Gas – Propane or Natural Gas.
Identification labels are found on the shipping box, and on
the rating plate which is located on the right side panel of
the cover. A so, each burner orifice is stamped with a number
(79 for LPG and 120 for Natura Gas).
Fig. 2 - Mounting the Heater
WALL STUDS
1” X 4”
SPACE BOARD
SUPPORT
BOARD
13 ¼”
Fig. 3 - Incandescent Particle Tray Illustration
The incandescent partic e tray (shipped oose in the carton
with the water heater) must be attached at the bottom of
the water heater front cover at the time of insta ation. Use
the screws provided. See figure 3
SCREWS
INCANDESCENT PARTICLE TRAY
appliance. The heater should never be common vented
with a mechanically vented appliance. Single wall vent
pipe is not recommended, if used consult the National
Fuel Gas Code.
Horizonta y venting to a sidewa vent terminator or a
vertica y constructed vent stack a ong an outside wa of a
bui ding is not permissib e. A Powervent (Mode AQ-1), with
a proof-of-draft safety inter ock device, is required and is
avai ab e in order to sidewa vent. Contact your dea er. In
the Commonwealth of Massachusetts: Powervented
applications must utilize proof-of-draft safety interlock
device.
VERTICAL GAS VENT: A 5 inch diameter gas vent constructed
of doub e wa Type B gas vent is recommended. 6 inch is
required in e evations greater than 2000 feet, see Fig. 4.
Any gas vent section that is greater than 45 degrees from
the vertica is considered horizonta . Horizonta sections must
s ope upwards at east ¼ inch for every foot of its horizonta
ength and be proper y supported. Keep the horizonta section
short and avoid too many e bows. The minimum vertica gas
vent height a owed is 6 feet; horizonta vent connectors
and e bows are not to be considered in the tota gas vent
height. A gas vent sections must be secured to each other
with sheet meta screws and be proper y supported.
The gas vent constructed of doub e wa Type B gas vent
must terminate above the roof surface with a isted vent
cap at a height that’s in accordance with Figure A or B and
their tab e, provided they are at east 8 feet (2.4 m) from a
vertica wa or simi ar obstruction. A other gas vents that
are not ab e to terminate within the minimum specified height
a owed must terminate not ess than 2 feet (0.6 m) above
the highest point where it’s passed through the roof and at
east 2 feet (0.6 m) higher than any vertica wa or simi ar
obstruction within 10 feet (3.1 m).

86 720 606 804
To check the draft:
C ose a doors and windows to the outside.
Turn on a app iances that force air out of the bui ding.
These inc ude a exhaust/venti ation fans, furnaces, c othes
dryers, wood burning stoves, etc.
Open a doors between the 125 HX and these other
app iances.
With the contro knob set fu y c ockwise and strong hot
water f ow rate, run the unit for at east 10 minutes. The
125 HX is equipped with a F ue Gas Sensor; it’s mounted
on the right side of the draft diverter (F ue Gas Sensor #34
on page 17). If the main burners shut off during this test it
is because the F ue Gas Sensor has detected inadequate
venting. This is a serious hea th hazard and must be corrected.
Poor venting can resu t in soot bui ding up inside the heater,
overheating of the heater and freezing of the heat exchanger
in a freezing environment, which is a a resu t of negative
air f ow. Additiona combustion air and/or improved venting
wi be necessary to correct this.
WARNING
Note: The burners of an instantaneous “on demand” water
heater such as the 125 HX are on y on at the time that hot
water is actua y being used, the vent pipe is therefore co d
except for the short durations when hot water is being used,
it is therefore very important that the venting and air supp y
be adequate to provide a good positive draft as soon as the
burners turn on.
The 125 HX instantaneous water heaters have bui t-in draft
diverters and are designed for indoor insta ation on y. The
MASONRY CHIMNEYS
Gas vent
Vent
connector
Establish a one foot
rise before any elbows
Listed vent cap
Figure C
MASONRY CHIMNEY: Masonry chimneys sha be bui t and
insta ed in accordance with NFPS 211 or oca codes. A
minimum 5” diameter gas vent pipe (meta doub e wa Type
B), or an approved c ay f ue iner or a isted chimney ining
system must be used when venting into a natura y drafting,
interna masonry chimney. 6 inch is required in e evations
greater than 2000 feet, see Fig. 4. Loca codes may require
the use of both gas vent and an approved ining system
when venting into a masonry chimney. The Commonwea th
of Massachusetts requires the use of a isted iner. Lining
systems inc ude approved c ay f ue ining, a isted chimney
ining system or other approved materia that wi resist
corrosion, erosion, softening, or cracking from exhaust f ue
gases at temperatures up to 1800 degrees F. The ining
system must be isted for use with natura y drafting, draft
hood equipped gas app iances. Fo ow oca codes and refer
to NFGC 54 and NFPA 58.
When connecting the water heater to a masonry chimney
the following connector guidelines must be followed for
safe and proper operation: An approved gas vent connector
must be attached to the top of the water heater and rise
vertica y at east 12” before entering into an approved gas
vent connector e bow. Any gas vent section that is greater
than 45 degrees from the vertica is considered horizonta .
If a horizonta vent connector is to be used to connect the
vertica gas vent connector on the top of the water heater
to the masonry chimney, that approved horizonta gas vent
connector must be kept as short as possib e and must be
s oped upwards at east ¼” per foot of its ength. This
connector must be supported throughout its horizonta ength.
This horizonta gas vent connection may be no greater than
75% of the tota vertica gas f ue vent within the chimney.
A so, an approved thimb e or co ar must be used when
penetrating a masonry chimney.
A) Existing INTERIOR Masonry Chimney
The meta gas vent pipe shou d be permanent y mounted
inside the masonry chimney. Doub e wa Type B gas vent is
recommended. The masonry chimney may have to be ti e
or meta ined before the insertion of the gas vent pipe;
check oca codes for c arification. The ining materia must
be isted for use on y with natura y drafting, draft hood
equipped gas app iances. Fo ow manufactures instructions
for insta ation of isted ining materia . You may not vent any
other fue burning app iances into any free space remaining
in the chimney. The minimum vertica gas vent ength within
the masonry chimney shou d be no ess than 5 ft (1.5 m);
the vent terminator shou d extend at east 3 feet (0.9 m)
above where the chimney meets the roof ine and at east 2
feet (0.6 m) higher than any vertica wa or simi ar obstruction
within 10 feet (3.1 m). The top of the gas vent shou d have
an approved vent terminator. See Figure C.
B) Tile Lined INTERIOR Masonry Chimney
The masonry chimney must have an approved iner, ceramic
ti e, c ay or meta . The masonry chimney must be ab e to
accommodate the spent fue gasses; consu t a venting
HVAC contractor for chimney capacity. A common venting
ike-fue app iance into this ined masonry chimney is
permissib e. The chimney’s diameter must be arge enough
to adequate y draft the spent fue gasses. A venting HVAC
contractor wi be required to spec a chimney system. The
minimum vertica chimney ength shou d be no ess than 5
ft (1.5 m); the termination point shou d extend at east 3
feet (0.9 m) above where the chimney meets the roof ine
and at east 2 feet (0.6 m) higher than any vertica wa or
simi ar obstruction within 10 feet (3.1 m). See Figure C.
C) EXTERIOR masonry Chimney
Refer to the Nationa Fue Gas Code and consu t a oca
venting HVAC contractor.

96 720 606 804
GAS CONNECTIONS
NOTE: The 125 HX is supplied with a gas pressure
regulator that must be installed on the heater before
attaching the gas supply line. See fig. 5. Failure to install
the gas regulator as shown in figure 5 will be a violation
of CSA certification of the unit. The regulator supplied
with the heater is preset for the gas shown on the rating
plate to the correct pressure. It is an appliance level
regulator designed for (low inlet) pressure (less than 1/
2 Psig or 15” W.C.)
DO NOT connect to an unregulated or high pressure
propane line or to a high pressure commercial natural
gas line.
GAS LINE SIZING
-It is strongly recommended that the Natural Gas pipe
be Black Iron pipe the entire distance from the outside
meter to the inlet of the 125 HX regulator. 1/2” Black Iron
pipe up to 10 feet, 3/4” Black Iron pipe up to 40 feet and
1” Black Iron pipe up to 150 feet distances. Flex line tubing
is NOT recommended, but if used then oversize it.
-It is strongly recommended that the LP Gas pipe be
semi-rigid copper or Black Iron pipe from the outside
regulator to the inlet of the 125 HX regulator. For semi-
rigid copper piping: 5/8” up to 20 feet and 3/4” up to 60
feet distances. For Black Iron piping: 1/2” up to 45 feet
and 3/4” up to 160 feet distances. Flex line tubing is NOT
recommended, but if used then oversize it.
THESE FIGURES ARE FOR 125 HX SUPPLY ONLY, ALL
OTHER APPLIANCES IN THE BUILDING WILL NEED TO
BE INCLUDED IN THE PIPE SIZING.
Nationa Fue Gas Code requires that a sediment trap (drip
eg) be insta ed on gas app iances not so equipped. The
drip eg must be accessib e and not subject to freezing
conditions. Insta in accordance with the recommendations
of the serving gas supp ier.
WARNING: The heater must be disconnected from
the gas supp y piping system during any pressure testing of
that system at test pressures in excess of 0.5 psig.
The water heater must be iso ated from the gas supp y piping
system by c osing the manua shutoff va ve during any
pressure testing of the gas supp y piping system at test
pressures equa to or more than 0.5 psig.
The water heater, inc uding the pressure regu ator provided
with it, must not be operated at gas supp y pressures in
excess of 0.5 psig. If overpressure has occurred, such as
through improper testing of the gas ines or ma function of
the supp y system, the gas va ve and regu ator must be
checked for safe operation. Make sure that the regu ator
vent is protected against b ockage.
When your connections are made, check for gas eaks at
a joints (not just the ones you made). App y some soapy
water to a gas fittings and gas va ve. Soap bubbles are a
sign of a leak.
NOTE: Do not app y soap so ution to the pi ot or pi ot orifice
area. If you have a eak, shut off the gas. After verifying that
required gaskets are in p ace, tighten appropriate fittings to
stop eak. Turn the gas on and check again with a soapy
so ution. Never test for gas leaks using a match or flame.
Fig. 5 - Installation of Gas Pressure Regulator
The pressure regu ator provided with the heater is adjusted
to de iver the proper gas pressure (as indicated on the rating
p ate and in the manua for a titude up to 2000 feet (660
meters) above sea eve . On app iances being insta ed above
2000 ft (660 meters) e evation, the in et gas pressure shou d
be set at insta ation to the va ue shown be ow.
draft diverter out et must be connected to an unobstructed
vent of the same size, or arger.
In Canada, CAN/CGA-B149 Insta ation Code for detai ed
requirements
In U.S.A., ANSI Z223.1 - NFPA 54, Nationa Fue Gas
Code for detai ed requirements.
The vent connection for the 125 HX is 5 inches. However,
for insta ations at high a titude (over 2000 feet above sea
eve ) a six inch vent is required. A 5" by 6" vent adaptor
must be affixed to the f ue co ar of the 125 HX with at east
two screws. See fig. 4.
WARNING: Fai ure TO INCREASE THE VENT SIZE
TO SIX INCHES AND/or assure that the manifo d pressure
is set to proper va ue isted for app ications at high a titudes
wi cause unsafe venting, asphyxiation, and wi void CSA
Certification.
Altitude Natural Gas Liquid Propane
inches W.C: inches W.C:
0' - 2.000 ft 5.7" 10.5"
2.000 ft - 4.500 ft 4.6" 8.4"
Above 4.500 ft consult your local gas provider.
MAXIMUM INLET GAS FLOW PRESSURE SETTING
Fig. 4 - Vent Adaptor for High Altitude Installations
5” X 6” ADAPTOR
USED ON HIGH ALTITUDE
NOTE: The gas pressures specified below refer to
pressures taken at the pressure tap on the gas inlet pipe
just above the regulator (See Fig 5). These readings
should be taken while the heater is operating at full input
— i.e. maximum water flow with the temperature dial
selector turned all the way clockwise.
GAS INLET PIPE
PRESSURE TAP
PRESSUREREGULATOR
(with directional arrow on
reverse side pointing
upward)
PLASTICVENTCAP

10 6 720 606 804
Nominal
Iron Pipe Black Iron Pipe
Size, Length of Pipe, Feet
Inches 10 20 30 40 50 60 70 80 90 100 125 150
1/2 275 189 152 129 114 103 96 89 83 78 69 63
3/4 567 693 315 267 237 217 196 185 173 162 146 132
1 107 732 590 504 448 409 378 346 322 307 275 252
1 1/4 220 149 121 103 913 834 771 724 677 630 567 511
1 1/2 330 229 185 155 141 127 118 108 102 976 866 787
2 622 433 346 299 264 239 220 204 192 1811 1606 1496
Copper
Outside Length of Tubing, Feet
Diameter,
Inch 10 20 30 40 50 60 70 80 90 100
3/8 39 26 21 19 _ _____
1/2 9262 5041 37 3531292726
5/8 199 131 107 90 79 72 67 62 59 55
3/4 329 216 181 145 131 121 112 104 95 90
7/8 501 346 277 233 198 187 164 155 146 138
GAS PIPING, CONNECTIONS and Gas Regulator
Before connecting the gas supp y, check the rating p ate on the right side of the front cover to be sure that the heater is
rated for the same gas to which it wi be connected.
In the United States: The insta ation must conform with oca codes or, in the absence of oca codes, the Nationa Fue
Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Insta ation shou d conform with CGA B149 INSTALLATION CODES and /or oca insta ation codes.
FOR NATURAL GAS
Maximum Capacity of pipe in Cubic Feet of Gas per Hour
for Gas Pressure of 0.5 Psig or ess and a Pressure drop of
0.3 in Water Co umn.
(Based on a 0.60 Specific Gravity Gas) Btu numbers given
in thousands.
GAS LINE SIZING
The gas supp y piping shou d be sized according to the App icab e P umbing Code for a maximum draw of 117,000 BTUH. First determine
the effective ength of the gas supp y ine by measuring the actua ength of piping, and then adding 5 ft. for every e bow or “T” to the actua
ength. Use the charts be ow to determine the pipe diameter necessary to accommodate the BTU demand of the unit. If there are more
gas drawing app iances on the ine, size according to the maximum amount of BTU demand.
Fo ow boxed numbers for piping just one 125 HX
(examp e: 3/4” B.I. Natura Gas pipe for 30 ft. wi hand e
152,000 btu’s). For mu tip e app iances combine the tota
btu input oad and then refer to app icab e chart be ow.
FOR LP GAS
Maximum Capacity of Pipe in Thousands of
BTU per Hour of Undi uted Petro eum Gases
(at 11 inches Water Co umn In et Pressure)
(Based on a Pressure Drop of 0.5 Inch Water
Co umn).
Maximum Capacity of Semi-Rigid
Tubing in Thousands of BTU per Hour of
Undi uted Liquified Petro eum Gases (at 11
inches Water Co umn In et Pressure)
(Based on a Pressure Drop of 0.5 Inch Water
Co umn)
* Source Nationa Fue Gas Code NFPA 54, ANSI Z223.1.
Nominal
Iron Length of Black Iron Pipe, Feet
Pipe Internal
Size, Diameter
inches inches 10 20 30 40 50 60 70 80 90 100 125 150 175 200
1/4 0.364 32 22 18 15 14 12 11 11 10 9 8 8 7 6
3/8 0.493 72 49 40 34 30 27 25 23 22 21 18 17 15 14
1/2 0.622 132 92 73 63 56 50 46 43 40 38 34 31 28 26
3/4 0.824 278 190 152 130 115 105 96 90 84 79 72 64 59 55
1 1.049 520 350 285 245 215 195 180 170 160 150 130 120 110 100
1 1/4 1.380 1050 730 590 500 440 400 370 350 320 305 275 250 225 210
1 1/2 1.610 1600 1100 890 760 670 610 560 530 490 460 410 380 350 320
2 2.067 3050 2100 1650 1450 1270 1150 1050 990 930 870 780 710 650 610
2 1/2 2.469 4800 3300 2700 2300 2000 1850 1700 1600 1500 1400 1250 1130 1050 980
3 3.068 8500 5900 4700 4100 3600 3250 3000 2800 2600 2500 2200 2000 1850 1700
4 4.026 17,500 12,000 9,700 8,300 7,400 6,80 6,200 5,800 5,400 5,100 4,500 4,100 3,800 3500

116 720 606 804
OPERATING INSTRUCTIONS
Before proceeding with the operation of the heater make
sure that the system is fi ed with water.
Open the co d water in et supp y to the heater fu y.
Open a hot water faucet to permit the water to fi the heater
and the piping and to e iminate the air trapped in the system
C ose the hot water faucet after the water f ows free y and
a the air has escaped from the system. The water heater is
now ready to operate.
FOR YOUR SAFETY READ BEFORE
OPERATING YOUR HOT WATER HEATER
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 app iance is equipped with e ectronic ignition for
ighting the pi ot and main burners. When turning the heater
on, fo ow these instructions exact y.
B. Before operating the unit, set the On/Off switch to the
On ( ) position. The On/Off switch is ocated behind
the f ip-down coverp ate on the front pane strip. Sme a
around the app iance area for gas. Be sure to sme next to
the f oor because some gas is heavier than air and wi sett e
on the f oor.
WHAT TO DO IF YOU SMELL GAS
- Do not try to ight any app iance.
- Do not touch any e ectric switch; do not use any phone
in your bui ding
- Immediate y ca your gas supp ier from a neighbor’s
phone. Fo ow the gas supp ier’s instructions.
- If you cannot reach your gas supp ier, ca the fire
department.
C. Use on y your hand to push in the on/off contro button.
Never use too s. Fo ow these instructions exact y. If contro
button is jammed, c ose the gas supp y and ca a qua ified
service technician. Attempted forcefu repair may resu t in a
fire or exp osion.
D. Do not use this app iance if any part has been under
water. Immediate y ca a qua ified service technician to
inspect the app iance and to rep ace any part of the contro
system and any gas contro which has been under water.
WATER CONNECTIONS
Insta the heater centra y in the bui ding if possib e and
make hot water piping runs as short as possib e When facing
the heater, the co d water in et wi be on the right and the
hot water out et on the eft.
A though water piping throughout the bui ding may be other
than copper, copper or ga vanized piping shou d be used
when connecting to the heaters ½” ma e NPT f ex connectors
(fo ow oca codes if more stringent). P astics or other PEX
type p umbing ine materia s are not suitab e for connecting
direct y to the water heater. Keep water in et pipe to no ess
than ½” (19.05mm) diameter to a ow the fu f ow capacity.
If the co d and hot connections to the heater are reversed,
the heater wi not function.
The 125 HX is provided with one f exib e type connector
that must be connected to the co d in et fitting of the water
va ve as shown in Fig. 6. The union end of the f exib e
connector shou d be attached to the rear in et port of the
water va ve with the supp ied washer gasket. No pipe dope
or thread tape is to be used at this joint. The ½” f exib e hot
water out et ine is supp ied attached to the heater.
Be certain there are no oose partic es or dirt in the piping.
B ow out or f ush the ines before connecting to the water
heater. Fu port va ves shou d be insta ed on both the co d
water supp y and hot water out et ines to faci itate servicing
the heater (see Fig. 7). For insta ation on a private we
system with the use of a pressure tank, the owest pressure
range setting recommended is 30-50 psi (2.07-3.45 bar).
Fig. 6 - Water valve - top view
Connecting the pressure relief valve (PRV)
A isted pressure re ief va ve supp ied with the heater must
be insta ed at the time of insta ation. No va ve is to be
p aced between the PRV and the heater. No reducing
coup ing or other restriction may be insta ed in the discharge
ine.
The discharge ine must be insta ed such that it a ows
comp ete drainage of both the PRV and the ine.
The ocation of the PRV must be readi y accessib e for
servicing or rep acement, and be mounted as c ose to the
water heater as possib e. See Fig 7. To insta the PRV, a
suitab e fitting connected to an extension on a “T” fitting
can be sweated to the hot water ine.
Support a piping.
Fig. 7 - Pressure Relief Valve
Pipe to
appropriate
discharge
Hot Co d

12 6 720 606 804
The position you se ect on the temperature adjustment knob
wi depend on the temperature of the incoming water (50°F
is average in the U.S.). In warm weather regions where the
incoming co d water is genera y warmer, or during the hot
weather months in some other areas a midway setting on
the temperature adjustment knob wou d produce a
temperature rise of about 70°F, giving an output of
approximate y 120°F. At this setting, if it is sti necessary,
one cou d mix a sma amount of co d water in a shower and
have a comfortab e shower at about 3 ga ons/minute. During
the co der months, or in co d c imate areas, it might be
necessary to set the contro to the maximum position, a
the way c ockwise to the right.
If you supply the 1 5 HX, with preheated water (i.e.) in a
solar installation the unit could overheat. It wi then shut off
on safety when the out et temperature reaches 194°F. For
this type of app ication, purchase a so ar mode 125B LPS
or 125B NGS.
If the in et water temperature to the water heater is very
warm the heater can produce temperatures that may be
found to be too hot. A temperature ba ance shower va ve
can automatica y mix in co d water to reduce such hot water
temperature, in the event of any temperature instabi ity with
the use of a temperature ba ance shower va ve, refer to
shower va ve manufactures instructions for interna
adjustment setting. Adjustments shou d be made to the
hottest setting in the shower va ve. Additiona y the
temperature contro of the heater can be adjusted to produce
a more comfortab e hot water temperature.
Fig. 8 - Temperature Adjustment Knob
LIGHTING AND OPERATING INSTRUCTIONS
1. STOP! Read the safety information above on this abe .
2. The gas va ve must be shut off by putting the ON/OFF
switch to position “ ”. Wait five (5) minutes to c ear
out any gas. If you sme gas, STOP! Fo ow “B” in the
safety information above. If you do not sme gas, go to
the next step.
3. This water heater is equipped with a safety pi ot burner
and an automatic ignition contro system.
4. Set the ON/OFF switch (f ip down cover p ate on front
pane strip) to the “ ” position. In this position, the
water heater is ready to use.
5. If the red LED indicator ight is f ashing, this is a warning
that the water pressure is not enough to ignite the main
burner.
6. Turn the hot water faucet on to the minimum f ow rate
required to activate the heater. The automatic ignition
system first ignites the safety pi ot burner which then
ignites the main burner in about 4 seconds.
7. The green LED indicator is on when the main burner is
on.
8. The pi ot f ame wi extinguish 10-30 seconds after the
burners come on. The burners wi remain on unti the hot
water tap is turned off.
NOTE: On a first time initia insta ation, existence of air in
the gas supp y ine and in the water ine may cause some
ignition de ay. In that case, repeated y open and c ose the
hot water tap in order to restart the ignition process unti a
the air has been purged.
TO TURN OFF GAS TO APPLIANCE
Turn off the manua ever on the gas supp y ine to the heater
and set the ON/OFF switch to the OFF ( ) position.
See Fig 9.
SETTING THE WATER TEMPERATURE
The 125 HX LP and 125 HX NG water heaters have a gas
contro that modu ates burner input in response to f ow. Its
purpose is to ensure that the hot water temperature wi
remain steady, a though the water f ow demand might vary
(down to 1/2 ga /minute). To adjust the temperature on your
125 HX, turn on a hot water faucet to its maximum f ow. At
the water heater, turn the arge knob ocated beneath the
main gas contro on the front of the heater a the way to the
right (c ockwise). See Fig 8. This wi produce a temperature
rise of approximate y 90°F at f ow rates between 0.5 and
2.0 ga ons per minute. Given that average incoming water
temperatures are 50°F, this heater wi produce
approximate y 140°F water at these f ow rates. Turning the
dia a the way to the eft (counterc ockwise) wi produce a
temperature rise of approximate y 45°F for f ow rates between
1.1 and 3.7 ga ons per minute. It is safest to se ect a
comfortab e temperature and not have to mix in co d water. Temperature Adjustment Knob
To start and to shut down
the appliance press the
button “ ”.
The switch is located
behind the flip down cover
plate on the front panel
strip.
G661_004
Decrease temperature
and increase flow
Increases temperature
and decreases flow
Fig. 9 - Principles of Operation
- on
- off
Green light on = main
burner on.
Green light off = main
burner off.
If the red light is flashing,
that means the water flow
is not enough to ignite
the burner.

136 720 606 804
Fig. 10 - Characteristic Pilot Flame
(Pi ot assemb y shown without pi ot hood)
MAINTENANCE AND SERVICE
REVIEW MAINTENANCE TABLE ON THE BACK OF THIS
MANUAL.
Approximate y once a year, the 125 HX shou d be checked
and c eaned. To remove the front cover, first remove the
incandescent partic e tray, then pu off the temperature
adjustment knob and unscrew and remove the p astic co ar.
Pu main cover out toward you and ift up and out. THE
FOLLOWING OPERATIONS SHOULD BE PERFORMED
BY A QUALIFIED SERVICE PERSON:
Vent System: Shou d be checked annua y. C ean and repair
as needed.
Water Valve (Part # 8707002649): The water va ve on this
heater shou d be serviced periodica y. Lubricate component
36 on page 18 with a sma amount of si icon, faucet or
ithium grease every two years to keep its o rings fresh and
pushrod s iding smooth y. Every 3-5 years rep ace component
36 on page 18. The frequency wi depend on the minera
content of the water and conditions of use or whenever
signs of corrosion appear at the gas and water va ve joint.
Periodica y check that the water in et fi ter (#27 on page
18) is c ean as we . NOTE: If water va ve is removed, be
sure to a so inspect the o ring sea on the end of the right
hand side water pipe before re-insta ing. Lubricating the o
ring with ithium or faucet and va ve grease is recommended.
Pilot Flame: The pi ot f ame shou d burn with a c ean, sharp,
b ue f ame and shou d resemb e the diagram in Fig. 10. If
the f ame is soft and ye ow, the pi ot burner orifice may
need to be c eaned or rep aced. The pi ot f ame shou d be
approximate y 2 inches ong, extending past the f ame sensor.
If the f ame is too sma , it wi not reach the f ame sensor
and the burners wi not come on.
Main Burner Flames: The main burner f ames shou d be
b ue, with a more intense b ue cone in the center core. Ye ow
f ames cou d be a sign of wrong size gas orifices or dirty
burners, or a b ockage on the heat exchangers fins. If some
burners have ye ow f ames whi e others have good f ames,
it is ike y that dust, int or spider webs have partia y c ogged
the burner venturis. To c ean the burners, contact a gas
service person.
Mineral Scale Build-up: The 125 HX heater, when operated
at ower temperature settings, does not accumu ate minera
bui d-up. If however, the heater is used at the higher
temperature settings and the water has a high minera
content, periodic desca ing may be necessary. The heating
coi s shou d be f ushed with a desca ing so ution. The
descaling is done only to the heat exchanger. The
chemica s wi damage the hydro-generator and other parts.
Consu t your service person.
TROUBLE SHOOTING
Introduction
The AquaStar 1 5 HX burners are activated by a water
flow valve. Numerous water related problems can cause
this water valve to malfunction such as: Insufficient water
flow volume to activate the burners at its minimum flow
requirement; Dirt in the water flow valve causing it to
malfunction; Sediment build-up in faucet aerators, or shower
heads; Uneven pressures between cold and hot. (with single
lever faucets) Plumbing cross overs. These water flow related
problems can cause the heater to deliver less than its full
output, or to fail to ignite or to shut down completely.
To clean the pilot burner and/ or the pilot orifice : Turn
off the gas to the unit. Set the On/Off switch to Off (position
). Remove the cover of the heater. To do so, pu off
the temperature adjustment knob and unscrew and remove
the p astic co ar. Pu main cover out toward you and ift up
and out. The pi ot orifice shou d be c eaned or rep aced. Do
not enlarge the orifice.
Do not use any wire or sharp object to c ean orifices. Natura
gas orifices are arge enough that you can usua y c ean
them by b owing through them. LP orifices, on the other
hand, are too sma to c ean and shou d be rep aced.
To access the pi ot orifice, remove 2 screws ho ding pi ot
assemb y in p ace. Then oosen compression fittings to expose
pi ot orifice.
3mm
Correct gap between pilot
burner tip and electrode tip
PiezoElectrode
Flame sensor
Piezo
Fig. 11 - Pilot burner with pilot orifice
(Pi ot assemb y shown without pi ot hood)
PILOTORIFICE

14 6 720 606 804
Prob ems are stated in upper case, bo d face. Most common
causes for the prob ems fo ow in order of ike ihood. The
suggested so utions require that the cover be taken off. To
do this, remove incandescent partic e tray, pu off the
temperature adjustment knob and unscrew and remove the
p astic co ar. Pu main cover out toward you and ift up and
out.
NO SPARK AT THE PILOT
1. On/Off switch is not ”On” (Position ).
The On/Off switch is ocated behind the f ipdown cover
p ate on the front pane strip. See fig. 9.
2. Cross over in water lines
To confirm there is no cross-over in the p umbing, shut off
the co d water supp y to the 125 HX and open a hot water
faucets. There shou d not be any water f owing at any faucets.
Water running is a sign of a p umbing cross-over. Consu t
your service person.
3. Water flow is not sufficient to activate heater.
Water f ow rate at faucet is be ow minimum f ow needed to
activate heater. When temperature adjustment knob is turned
a the way c ockwise, the mode 125 HX requires 1/2 ga on
per minute f ow to activate the heater. As a reference, this
is a f ow which wou d fi a quart jar in 30 seconds. If the
temperature adjustment knob is turned fu y
counterc ockwise, a f ow rate of 1.1 ga ons/minute is required
to activate the heater.
The red LED ight ( ocated behind the coverp ate on the
front pane ) f ashes when the water f ow is not enough.
4. Water inlet filter is clogged
Water f ow is restricted, preventing needed f ow to activate
heater. C ean water in et fi ter screen.
5. Cold incoming water connection made to wrong side
of heater
Make sure co d water in et connection is on the right side of
heater when you are facing heater.
6. Water valve parts may be dirty or components damaged
First check that venturi is free of dirt partic es. Water va ve
and component parts must be tota y free of dirt. In hard
water areas, minera deposits can eventua y (3-5 years in
hard water areas) corrode the water va ve parts to a point
where they wi need rep acing. Any sign of moisture or
corrosion at the joint of the water valve and the gas valve is
a sign that the water valve components need to be serviced
immediately.
7. Poor circuit connections at the ECO (overheat sensor)
or the flue gas safety device
Ignition sparker wi not operate if the e ectrica circuit is
interrupted. Check that the connections to the ECO and
F ue Gas Safety Device are secure and tighten if necessary.
If the 1 5 HX is Powervented, check spill switch reset
SPARK APPEARS AT PILOT WHEN HOT WATER TAP
TURNED ON, BUT PILOT AND BURNERS WILL NOT IGNITE
1. Air in the Gas Line
Norma y this is a prob em at time of initia insta ation, after
the pipes have been worked on, or after a gas supp y ine
has been a owed to empty. B eed the air trapped in the gas
ine by turning the hot water faucet on and off unti the air
has been c eared from the ine.
2. No gas to the 125 HX
A. Gas cock on gas ine may not be open
B. Gas regu ator may be shut or damaged. Rep ace or un ock
the regu ator. Note: The regu ator furnished with the heater
is exc usive y designed for ow gas pressure. Excessive
pressure wi ock it up. Locking usua y happens when using
propane gas if the gas pressure between the gas tank and
the water heater’s gas regu ator has not been reduced. See
Page 3 for recommended correct gas pressure. To un ock a
regu ator, consu t your service person.
3. Pilot orifice or gas valve is dirty
C ogging of the pi ot burner can be caused by dust in the
air or dirt in the gas. The pi ot orifice or gas fi ter may need
to be c eaned or rep aced.
4. Pilot electrovalve switch may need to be replaced (See
Fig 13).
Measure mi ivo tage at pi ot e ectrova ve (see Fig. 13).
5. Electronic Control Box may need to be replaced (See
Fig 13).
Check wire connections and test operation of e ectronic
contro box (see Fig. 13).

156 720 606 804
Fig. 13 - Electrical wiring diagram
5. Flue gas safety device tripped
Venti ate the room and operate the app iance 10 minutes
ater. Provide more combustion air to the room and/or inspect
and correct venting system. Afterwards, if it happens again,
contact your service person.
WATER IS TOO HOT
1.Temperature Selection too high
Turn the temperature adjustment knob counter-c ockwise
(to the eft) to ower the maximum water temperature.
Note: This will increase the activation flow rate.
2. Inlet water temperature is too hot (as with solar
preheated water or high ground water temperatures)
Decrease gas pressure. Note: On y the mode 125B LPS or
125B NGS shou d be used if the in et water is preheated.
3. Ground water temperature is very warm
Reduce in et gas supp y to heater when in et water
temperature is very warm (60-70 F). See a so HOT WATER
TEMPERATURE FLUCTUATES / UNIT DEACTIVATED.
WATER IS NOT HOT ENOUGH
1. Temperature selection too low.
Change the setting. Turn the temperature adjustment knob
c ockwise (to the right).
Note: This will decrease the activation flow rate.
2. Btu input is too low due to insufficient gas pressure
It is extremely important for a tankless instantaneous
water heater to have the right size gas line to obtain
the correct gas pressure
See specifications on page 3. Un ike storage tank water
heaters, the burners of a tank ess water heater must be very
powerfu to heat water instantaneous y since they do this
on y at the time hot water is actua y being used. It is therefore
imperative that the gas pressure requirement be met exact y.
Insufficient gas pressure wi direct y affect the water
temperature at the time of usage. See page 3 for correct
gas pressure settings and fig. 5 for ocations where gas
pressures are taken.
3. Btu input is too low due to insufficient gas supply
Make sure your main gas ine is fu y opened. If using LP
gas, be sure that the size of the propane tank is adequate to
supp y the required gas pressure.
4. Cold water is mixing with the hot water between the
125 HX and the outlet
Compare water temperature at out et of the 125 HX (ho d
the 125 HX out et pipe with your hand) and at the tap. If
these two are very different, check for mixing va ve or
p umbing crossover (see “NO SPARK AT THE PILOT”
paragraph #2).
5. Parts in water valve are dirty or damaged, which will
prevent the gas valve from being fully opened.
Water va ve maintenance needs to be performed, see #6
under NO SPARK AT THE PILOT
PILOT LIGHTS BUT BURNERS WILL NOT COME ON
1. Confirm water valve assembly is working properly.
See Water Va ve under MAINTENANCE AND SERVICE.
2. Confirm the flame sensor is in its proper position and
clean, lightly wipe clean if dirty. See Fig. 10
3. Confirm the burner electrovalve switch is functioning
properly.
Measure mi ivo tage at burner e ectrova ve (see Fig. 13).
4. The Electronic Control Box (Fig. 13) may need to be
replaced.
Check wire connections and test operation of e ectronic
contro box (see Fig. 13).
8 e ectronic contro box
9 LED fai ure indicator
10 LED indicator main
burner operation
11 on/off switch
12 hydro-generator
13 f ue gas safety device
1 burner e ectrova ve
2 gas contro va ve
3 pi ot e ectrova ve
4 f ame sensor
5 pi ot e ectrode
6 overheat sensor
7 temperature imiter
MAIN BURNERS GO OUT DURING HOT WATER USE
1. Flow rate diminished below activation rate
Increase hot water f ow rate.
2. Unbalanced pressure in the water lines
The added restriction caused by the 125 HX in the hot water
system can resu t in uneven pressures between the co d
and the hot. In such cases when mixing co d water at the
tap, the ower hot water pressure may be overpowered by a
much higher co d water pressure, which may cause the 125
HX burners to shut down. Make sure faucet aerators and
showerheads are free of minera s and dirt. Do not add any
f ow restrictor to the shower head.
3. Minimum inlet pressure on well is inade uate
Check the in et water pressure. On a private we , raise the
minimum pressure setting to 30 psi. Confirm that the
pressure tank is not water ogged.
4. ECO (overheat sensor) tripped due to overheating
re-ignite the app iance 10 minutes ater. If it happens again,
contact your service person.

16 6 720 606 804
HOT WATER TEMPERATURE FLUCTUATES / UNIT
DEACTIVATED
1. Unbalanced pressure in waterlines
The added restriction caused by the 125 HX in the hot water
system can resu t in uneven pressures between the co d
and the hot. In such cases when mixing co d water at the
tap, the ower hot water pressure may be overpowered by a
much higher co d water pressure, which may cause the 125
HX burners to shut down. Make sure faucet aerators or
shower heads are free of minera s. Do not add any flow
restrictor to the shower head.
2. Temperature balance valves
If the in et water temperature to the water heater is very
warm the heater can produce temperatures that may be
found to be too hot. A temperature ba ance shower va ve
can automatica y mix in co d water to reduce such hot water
temperature, in the event of any temperature instabi ity with
the use of a temperature ba ance shower va ve, refer to
shower va ve manufactures instructions for interna
adjustment setting. Adjustments shou d be made to the
hottest setting in the shower va ve. Additiona y the
temperature contro of the heater can be adjusted to produce
a more comfortab e hot water temperature. See SETTING
THE WATER TEMPERATURE section.
3. Cold water is mixing with the hot water between the
125 HX and the outlet
See #2 under “NO SPARK AT THE PILOT”.
4. Inlet water pressure is erratic due to inade uate supply
water pressure or saturated pressure tank on well
system
Check the in et water pressure. For insta ation on a private
we system with the use of a pressure tank, the owest
pressure range setting recommended is 30-50 psi (2.07 -
3.45 bar). Confirm that the pressure tank is not water ogged.
5. Gas pressure is too low
See page 3 for correct specifications.

176 720 606 804
Fig. 14 - Diagram of 125 HX
1. Heat exchanger
2. Pi ot assemb y
3. Burner manifo d gas
pressure test nipp e
4. Main gas burner
5. Pi ot gas tubing
6. LED fai ure indicator
7. on/off switch
8. LED operation indicator
9. Water va ve
10. Temperature adjustment se ector
11. Gas in et gas pressure test nipp e
12. Hose
3
1
4
10
11
2
9
8
6
7
5
12
6 720 606 804-10.1AL

18 6 720 606 804
Fig. 15 - INTERIOR COMPONENTS DIAGRAM AND PARTS LIST

196 720 606 804
Fig. 15
INTERIOR COMPONENTS DIAGRAM
AND PARTS LIST 125 HX
1 Cover 8 705 421 752
2 Temperature adjustment knob 8 702 000 111
3 Temperature adjustment collar 8 700 403 008
4 Draft diverter 8 705 505 354
5 Heat exchanger 8 705 406 235
7 Main burner 8 708 120 298 NG
7 Main burner 8 708 120 296 LP
8 Burner assembly washer 8 710 103 060
9 Throttle disc 8 700 100 174 LP
10 Pilot burner 8 708 105 491 LP
10 Pilot burner 8 718 105 051 NG
11 Pilot electrode 8 708 107 006
12 Pilot orifice 8 708 200 069 NG
12 Pilot orifice 8 708 200 312 LP
13 Pilot tube 8 700 707 370
14 Washer pilot tube 8 700 103 173
15 Gas valve 8 707 011 917 NG
15 Gas valve 8 707 011 945 LP
16 Diaphragm switch 8 708 504 021 NG
16 Diaphragm switch 8 708 504 049 LP
17 Pilot electrovalve 8 708 501 249
18 Burner electrovalve 8 708 501 250
19 O-ring 8 700 205 023
20 Hydro-generator 8 707 406 043
21 Cold water pipe 8 700 705 947
22 Outlet flex hose 8 700 703 139
23 Washer 8 700 103 658
24 Water valve 8 707 002 649
25 Water valve cover 8 705 500 101
26 Diaphragm 8 700 503 053
27 Water inlet filter 8 700 507 001
28 Water valve selector screw 8 708 500 289
29 Volumetric water governor 8 705 705 009
30 Venturi 8 708 205 279
31 Electronic control box 8 707 207 085
32 Flame sensor cable 8 704 404 040
33 Electrode cable 8 704 404 039
34 Flue Gas Sensor 8 707 206 345
35 Set of cables 8 704 404 038
36 Pushrod 8 700 306 114
37 O-ring 8 700 205 120
38 O-ring 8 700 205 119
39 Water connection gasket 8 710 103 043
40 Water elbow fitting 8 700 703 114
41 Overheat sensor (ECO) 8 707 206 040
42 Connecting pipe hot 8 700 715 178
43 Washer 8 710 103 045
44 Flame sensor 8 708 107 007
45 Water valve set screw 8 703 401 051

20 6 720 606 804
Fig. 16 - Flow chart of 125 HX