Bosch 125B NGS, 125B LPS Installation And Operating Instructions Manual

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 qualified
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.

FEATURING: Automatic Variable Power Modulating Gas
Valve with Thermostatic Control
Warning: If you do not follow these instructions exactly, a
fire or explosion may result causing property damage,
personal injury or loss of life.

INSTALLATION AND OPERATING INSTRUCTIONS FOR AUTOMATIC
INSTANTANEOUS TYPE WATER HEATERS FOR USE WITH NATURAL AND
LIQUEFIED PETROLEUM GAS

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 liquids 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
qualified installer, service agency or the gas supplier.

Specifications................................................................. Page 2

Rules for safe operation ...............................................Page 4

Locating the Heater ......................................................Page 4

Combustion Air Requirements ....................................Page 5

Mounting the Heater .....................................................Page 6

Venting the Heater ........................................................Page 7

Gas Connections ....................................................... Page 10

Water Connections .................................................... Page 11

Safety before lighting the pilot ................................ Page 12

Lighting instructions ................................................... Page 12

Information on water temperature ........................... Page 13

Maintenance & Service ............................................. Page 13

Trouble Shooting ......................................................... Page 14

Diagram of AquaStar .................................................. Page 17

Components and Parts List ...................................... Page 19

Warranty ....................................................................... Page 21

TABLE OF CONTENTS

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MODEL 125B LPS and 125B NGS (Thermostatically Modulated)

Suitable for heating potable water only

Not approved for space heating purposes

Intended for domestic hot water with preheated inlet water as with solar hot water.

2 6 720 606 518

This well engineered, gas water heater has been specially
designed to operate with incoming pre-heated water:

It operates on the principle of heating water instantaneously
“on demand”. When a hot water faucet is opened, cold water
flows through the coils of the heat exchanger in the Aquastar.
This same flow opens the gas valve, and the burners are
ignited by the pilot flame. The heat exchanger coils absorb
the heat generated by the burners and transfer heat to the
water. When the hot water faucet is shut off, the gas valve
automatically closes and the burners turn off. Your hot water
faucet is an ignition key to turn on the water heater, giving
you control over your hot water energy use. Each time you
turn off your hot water faucet, you also shut off the water
heater. On the Aquastar “S” model, if the incoming water is
colder than the thermostat setting of the heater, the burners
will ignite to heat the water in order to boost it and maintain
it at the temperature setting. If the incoming water has been
pre-heated, (ie) solar, and this water temperature is warm
then the the burners will modulate down accordingly, or
shut down completely if the temperature is as hot or hotter
than the heater thermostat setting. The Aquastar 125 BS is
the perfect backup to a solar hot water system.

FEATURES

- High Quality Materials for Long Working Life.

- Copper heating coils for endless supply of hot water.

- Burner output proportional to hot water flow demand for
maximum energy efficiency.

- Automatic Thermostatic Control for steady hot water
temperature

- Input BTU’s modulate to zero to prevent overheating of
water from pre-heat source

- Safety thermocouple at pilot burner.

- Automatic overheating protection shut-off sensor.

- Stainless steel burners with stabilized blue flame.

- Built-in corrosion resistant draft inducer.

- Compact space saver: mounts on a wall with two hooks.

- Easily removable one-piece cover.

- Easy one person installation.

- Adjustable water flow restrictor to ensure that water flow
demand will not exceed the heating capacity of the heater.

- Easy pilot flame lighting with push button piezo ignition.

BOSCH is constantly improving our products, therefore
specifications are subject to change without prior notice.

AquaStar 125B LPS and 125B NGS Specifications

Gas Input max.: 117,000 Btu/hr

min.: 23,400 Btu/hr

Water Connection 1/2” 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 44 LB

Net Weight 42 LB

1.8 GPM at 90° rise

3.7 GPM at 45° rise

Min. Water Flow 1/2 gal/min

LP GAS Supply Pressure
(before Aquastar regulator) min.: 11” W.C.

max.: 14” W.C.*

Required LP GAS Pressure at inlet
tap while Aquastar is operating: 10.5” W.C.

LP GAS Burner Manifold pressure while Aquastar
is operating at maximum input: 9.0” W.C.

Natural Gas Supply Pressure
(before Aquastar regulator) min.: 7” W.C.

max.: 14” W.C.*
Required Natural Gas Pressure at inlet tap
while Aquastar is operating: 5.7” W.C.

Natural Gas Burner Manifold pressure while Aquastar is
operating at maximum input: 4.2” W.C.

* Inlet gas pressure before Aquastar regulator must not
exceed this value. Pressure may need to be adjusted for
high altitudes, see page 11.

UNPACKING THE AQUASTAR HEATER

This heater is packed securely. The box includes two water
connection fittings, a gas pressure regulator, a pressure relief
valve, an incandescent particle tray, two hooks for hanging
the heater, this manual, a warranty statement and a warranty
registration card. Do not lose this manual, as there is a
charge for replacement. Please complete and return the
enclosed warranty registration card.

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D861_059

MINIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON

COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS

FRONT VIEW SIDE VIEW

AQUASTAR MODEL 125BS

MODEL 125BS

TOP (A) 12 "
FRONT (B) 4 "
BACK 0 "
SIDES 4 "
FLOOR (C) 12 "
VENT DIAMETER 5 "

4 6 720 606 518

PROPER LOCATION FOR INSTALLING YOUR
HEATER

Carefully select the location of your new heater. For your
safety and for proper heater operation, you must provide an
abundant supply of combustion air and a proper venting
installation.
The heater may still operate even when improperly vented.
It will, however, be less efficient and could eventually damage
the heater. It could even result in human sickness or death
due to oxygen deprivation and carbon monoxide poisoning.
Follow the guidelines below:

1. Place your heater as close to a vent or chimney as
possible.

2. National building codes require that you do not install
this appliance in bathrooms, bedrooms, unvented closet or
any occupied rooms normally kept closed.

3. Simultaneous operation of other appliances such as
exhaust fans, ventilation systems, clothes dryers, fireplaces
or wood stoves could create a vacuum effect in your home
which could cause dangerous combustion by-products to
spill back into your home rather than venting to the outside
through the flue. Confirm that your Aquastar is venting
properly when all these other appliances are running. See
section on venting.

Do not obstruct the flow of combustion and ventilation
air to the appliance. If installed near a clothes dryer it is

very important that the dryer be properly vented. Failure to
properly vent a dryer could result in a gradual accumulation
of lint on the water heater fin coils and burners, leading to a
dangerous condition of vent blockage and poor unsafe
combustion.

4. Your hot water lines should be kept short to save energy.
It is always best to have hot water lines insulated.

WARNING: The water in this water heater is cold

and always remains cold 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 not approved for
outside installation. Drain the heater entirely if freezing

temperatures are anticipated in the area where heater is
installed by disconnecting both the inlet and outletelbow
connections at the rear of heater. Additionally remove the
drain plug under the water valve. See Fig 0.

GENERAL RULES TO FOLLOW
FOR SAFE OPERATION

1. You should follow these instructions when you install your

heater. In the United States: The installation must conform
with local codes or, in the absence of local codes, the
National Fuel Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Installation should conform with CGA
B149.(1,2) INSTALLATION CODES and/or local installation
codes.

2. Carefully plan where you install the heater. Correct
combustion air supply and flue pipe installation are very
important. If not installed correctly, fatal accidents can be
caused by lack of air, carbon monoxide poisoning or fire.

3. The place where you install the heater must have enough
ventilation. The National Fire Codes do not allow gas fired
water heater installation in bathrooms, bedrooms or any
occupied rooms normally kept closed. See the section below
on locating the heater.

4. You must vent your heater. See section on VENTING,
Page 6.

5. The appliance must be disconnected from the gas supply
piping system during any pressure testing at pressures in
excess of 1/2 Psig (3.5 kPa).
The appliance must be isolated from the gas supply piping
system by closing its individual manual shutoff valve during
any pressure testing of the gas supply piping system at test
pressures equal to or more than 1/2 Psig (3.5Kpa). The
appliance and its gas connection must be leak tested before
placing the appliance in operation.

6. Keep water heater area clear and free from combustibles
and flammable liquids. Do not locate the heater over any
material which might burn.

7. Correct gas pressure is critical 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, while all the other gas
appliances are in operation. Check with your local gas
supplier, and see the section on connecting the gas supply.

8. Should overheating occur or the gas supply fail to shut
off, turn off the gas supply at the manual gas shut off valve
on the gas line.

9. Do not use this appliance if any part has been underwater.
Immediately call a qualified service technician to inspect
the appliance and to replace any part of the control system
and any gas control which has been underwater.

This product is not approved for manufactured homes
(mobile home), recreational vehicles (RV) or boats.
Reference ANSI Z21.10.3.
This product is neither designed or approved for outside
installations.

Fig. 0 - Water heater drain plug

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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 liquids.

COMBUSTION AIR REQUIREMENTS

The AquaStar water heater holds cold water in its copper
heat exchanger and brass water valve when not in use.
Because of this, any cold air that comes in through the
unit’s vent pipe is capable of freezing these components.
This Installation Manual specifies the minimum vertical vent
pipe and the amount of combustion air required for this unit.
When all requirements are followed, the unit will operate
properly and safely. However, there may still be a risk of
freezing due to negative draft if all the combustion appliances
in the area are not being supplied with a sufficient amount
of make-up air. A wood stove or furnace can rob the make­up air in the AquaStar’s vent pipe, leaving the cold infiltrating
air capable of freezing the cold water in the AquaStar heat
exchanger. More make up air is the solution. Follow the
instructions on venting and checking adequacy of make up
air. A HVAC specialist should be used to design solutions
for providing more make-up air if necessary.

Observe the following instructions concerning combustion
air.

Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater

than 50 cubic feet per 1000 Btu per hour of the combined
rating of all appliances installed in the space. That would
be 5850 cubic feet for the AquaStar 125B “S” alone.

b) In unconfined spaces in buildings of conventional frame,

masonry, or metal construction, infiltration is normally
adequate to provide air for combustion, ventilation, and
dilution of flue gasses.

Appliances located 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
enclosure. Each opening must have a minimum free area of
one square inch per:

- 1000 Btu/hr if all air is taken from inside the building.

- 2000 Btu/hr if all air is taken from the outside by horizontal

ducts.

- 4000 Btu/hr if all air is taken from the outside by direct

openings or vertical ducts.
Or the confined space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of the
enclosure. This opening must have a minimum free area of
one square inch per:

- 3000 Btu/hr if all air is taken from the outside by a direct
opening or vertical duct.

Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of your
openings by 75% if your louvers are wood and by 30% if
your louvers are metal. Refer to the National Fuel Gas Code
for complete information. In buildings of tight construction
all air should be taken from outside.

CLEARANCES

The Aquastar 125 B “S” is design certified for installation
on a combustible wall and for installation in an alcove or
closet with the minimum clearances to combustible and non

-combustible construction listed below

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)

Clearance from vent is dependent upon the clearance rating
of the venting material used. For example, type B-a vent is
approved for 1 inch clearance.

Note: Typically, the minimum clearance to combustible
materials should not be less than 6” for single wall flue
pipe. Note that this clearance can be reduced if combustible
materials are protected as per table VI of the National Fuel
Gas Code or if Type B gas vent is used.

125BS

Air Vents

(5 ½ X 5 ½ in. each)

Air Vents

(10 ¾ X 10 ¾ in. each)

125BS

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Fig. 1 - Mounting the Heater

Fig. 2 - Incandescent Particle Tray Illustration

The incandescent particle tray (shipped loose in the carton
with the water heater) must be attached at the bottom of
the water heater front cover at the time of installation. Use
the screws provided. See figure 2

SUPPORT BOARD

WALL STUDS

1” X 4”

SPACE BOARD

13 ¼”

SCREWS

INCANDESCENT PARTICLE TRAY

MOUNTING INSTALLATION

The Aquastar 125 B “S” is design certified for mounting on
a wall.
Secure the two L shaped hooks provided with the heater to
a wall surface. Place them 13 ¼ inches apart as shown in
Fig 1. Do not install this appliance on a carpeted wall or
over floor covering which is combustible, such as carpet.
The heater must be mounted on a wall using appropriate
anchoring materials. If wall is a stud wall sheathed with
plasterboard, 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 1.

Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted directly to a brittle, friable board, such as
plasterboard, can cause failure of mounting.
In earthquake-prone zones, BBTNA recommends that
installers use a large washer and lag screw through the
existing holes used to hang the heater to affix the upper
third of the heater to the mounting board. To affix the lower
third of the heater, BBTNA recommends that two new holes
be drilled in the heater’s frame, each one 16 inches below
the top two holes, and that washers and lag screws be used
to secure the lower 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. Also, each burner orifice is stamped with a number
(79 for LPG and 120 for Natural Gas).

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VENTING

Vent pipe connection. WARNING: Do not reduce the vent pipe size. See Fig. 3 for high altitude installations

The heater must be vented to the outside following all local ordinances and specifications for installing a gas appliance
vent or chimney. The heater must be located as close as practicable to a vertically rising chimney or vent that has a listed
vent cap at its termination point. The venting system must be designed and constructed so as to develop a positive flow
adequate to remove flue gasses to the outdoors.

Consult the National Fuel Gas Code if the vent will have elbows or share venting with another natural draft 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.

Horizontally venting to a sidewall vent terminator or a vertically constructed vent stack along an outside wall of a building
is not permissible. A Powervent (Model AQ-1), with a proof-of-draft safety interlock device, is required and is available in
order to sidewall vent. Contact your dealer. 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 double wall Type B gas vent is recommended. 6 inch is

required in elevations greater than 2000 feet, see Fig. 3. Any gas vent section that is greater than 45 degrees from the
vertical is considered horizontal. Horizontal sections must slope upwards at least ¼ inch for every foot of its horizontal
length and be properly supported. Keep the horizontal section short and avoid too many elbows. The minimum vertical gas
vent height allowed is 6 feet; horizontal vent connectors and elbows are not to be considered in the total gas vent height.
All gas vent sections must be secured to each other with sheet metal screws and be properly supported.

The gas vent constructed of double wall Type B gas vent must terminate above the roof surface with a listed vent cap at
a height that’s in accordance with Figure A or B and their table, provided they are at least 8 feet (2.4 m) from a vertical wall
or similar obstruction. All other gas vents that are not able to terminate within the minimum specified height allowed must
terminate not less than 2 feet (0.6 m) above the highest point where it’s passed through the roof and at least 2 feet (0.6
m) higher than any vertical wall or similar obstruction within 10 feet (3.1 m).

LISTED VENT CAP

LISTED VENT CAP

LISTED GAS VENT

LOWEST DISCHARGE OPENING

H (minimum) height
from roof to lowest
discharge opening

Figure A Figure B

ROOF PITCH

IS X/12

12

X

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

8 6 720 606 518

MASONRY CHIMNEY: Masonry chimneys shall be built and installed in accordance with NFPS 211 or local codes. A

minimum 5” diameter gas vent pipe (metal double wall Type B), or an approved clay flue liner or a listed chimney lining
system must be used when venting into a naturally drafting, internal masonry chimney. 6 inch is required in elevations
greater than 2000 feet, see Fig. 3. Local codes may require the use of both gas vent and an approved lining system when
venting into a masonry chimney. The Commonwealth of Massachusetts requires the use of a listed liner. Lining systems
include approved clay flue lining, a listed chimney lining system or other approved material that will resist corrosion,
erosion, softening, or cracking from exhaust flue gases at temperatures up to 1800 degrees F. The lining system must be
listed for use with naturally drafting, draft hood equipped gas appliances. Follow local 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

vertically at least 12” before entering into an approved gas vent connector elbow. Any gas vent section that is greater than
45 degrees from the vertical is considered horizontal. If a horizontal vent connector is to be used to connect the vertical
gas vent connector on the top of the water heater to the masonry chimney, that approved horizontal gas vent connector
must be kept as short as possible and must be sloped upwards at least ¼” per foot of its length. This connector must be
supported throughout its horizontal length. This horizontal gas vent connection may be no greater than 75% of the total
vertical gas flue vent within the chimney. Also, an approved thimble or collar must be used when penetrating a masonry
chimney.

A) Existing INTERIOR Masonry Chimney

The metal gas vent pipe should be permanently mounted inside the masonry chimney. Double wall Type B gas vent is
recommended. The masonry chimney may have to be tile or metal lined before the insertion of the gas vent pipe; check
local codes for clarification. The lining material must be listed for use only with naturally drafting, draft hood equipped gas
appliances. Follow manufactures instructions for installation of listed lining material. You may not vent any other fuel
burning appliances into any free space remaining in the chimney. The minimum vertical gas vent length within the masonry
chimney should be no less than 5 ft (1.5 m); the vent terminator should extend at least 3 feet (0.9 m) above where the
chimney meets the roofline and at least 2 feet (0.6 m) higher than any vertical wall or similar obstruction within 10 feet (3.1
m). The top of the gas vent should have an approved vent terminator. See Figure C.

B) Tile Lined INTERIOR Masonry Chimney

The masonry chimney must have an approved liner, ceramic tile, clay or metal. The masonry chimney must be able to
accommodate the spent fuel gasses; consult a HVAC engineer for chimney capacity. A common venting like-fuel appliance
into this lined masonry chimney is permissible. The chimney’s diameter must be large enough to adequately draft the spent
fuel gasses. See NFPA 54 for guidelines. A HVAC engineer will be required to spec a chimney system. The minimum
vertical chimney length should be no less than 5 ft (1.5 m); the termination point should extend at least 3 feet (0.9 m)
above where the chimney meets the roofline and at least 2 feet (0.6 m) higher than any vertical wall or similar obstruction
within 10 feet (3.1 m). See Figure C.

C) EXTERIOR masonry Chimney

Refer to the National Fuel Gas Code and consult a local HVAC professional.

MASONRY CHIMNEYS

GAS

VENT

LISTED VENT CAP

VENT CONNECTOR

ESTABLISH A ONE

FOOT RISE BEFORE

ANY ELBOWS

Figure C

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Fig. 3 – Vent Adaptor for High Altitude Installations

5” X 6” ADAPTOR

USED ON HIGH ALTITUDE

To check the draft:

Close all doors and windows to the outside.
Turn on all appliances that force air out of the building.
These include all exhaust/ventilation fans, furnaces, clothes
dryers, wood burning stoves, etc.
Open all doors between the AquaStar and these other
appliances.
Run the unit for at least 10 minutes. Then hold an ordinary
mirror at the side above the front shell. Any flue gases
backdrafting will cause the mirror to fog. This is a serious
health hazard and must be corrected. Poor venting can result
in soot building up inside the heater, overheating of the heater
and freezing of the heat exchanger in a freezing environment.
The mirror will remain clear with a properly functioning draft.

WARNING

Note: The burners of an instantaneous “on demand” water

heater such as the AquaStar are only on at the time that
hot water is actually being used, the vent pipe is therefore
cold except for the short durations when hot water is being
used, it is therefore very important that the venting and air
supply be adequate to provide a good positive draft as soon
as the burners turn on. See venting guide on back page.

The AquaStar 125B”S” instantaneous water heaters have
built-in draft diverters and are designed for indoor installation
only. The draft diverter outlet must be connected to an
unobstructed vent of the same size, or larger.

In Canada, CAN/CGA-B149 Installation Code for detailed
requirements
In U.S.A., ANSI Z223.1 - NFPA 54, National Fuel Gas
Code for detailed requirements.

The vent connection for the Aquastar 125BS is 5 inches.
However, for installations at high altitude (over 2000 feet
above sea level) a six inch vent is required. A 5” by 6” vent
adaptor must be affixed to the flue collar of the Aquastar
with at least two screws. See Fig. 3.

WARNING: Failure TO INCREASE THE VENT

SIZE TO SIX INCHES AND/or assure that the manifold
pressure is set to proper value listed for applications at high
altitudes will cause unsafe venting, asphyxiation, and will
void CSA Certification.

10 6 720 606 518

GAS CONNECTIONS and Gas Regulator

NOTE: The Aquastar 125 B”S” is supplied with a gas pressure regulator that must be installed on the heater before
attaching the gas supply line. See figure 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.

FOR NATURAL GAS

Maximum Capacity of pipe in Cubic Feet of Gas per Hour
for Gas Pressure of 0.5 Psig or less and a Pressure drop of

0.3 in Water Column.
(Based on a 0.60 Specific Gravity Gas) Btu numbers given
in thousands.

Follow boxed numbers for piping just one Aquastar 125BS
(example: 3/4” B.I. Natural Gas pipe for 30 ft. will handle
152,000 btu’s). For multiple appliances combine the total
btu input load and then refer to applicable chart below.

FOR LP GAS

Maximum Capacity of Pipe in Thousands of
BTU per Hour of Undiluted Petroleum Gases
(at 11 inches Water Column Inlet Pressure)
(Based on a Pressure Drop of 0.5 Inch Wa­ter Column).

Maximum Capacity of Semi-Rigid
Tubing in Thousands of BTU per Hour of
Undiluted Liquified Petroleum Gases (at 11
inches Water Column Inlet Pressure)

(Based on a Pressure Drop of 0.5 Inch Water
Column)

* Source National Fuel Gas Code NFPA 54, ANSI Z223.1 - No
Additional Allowance is necessary for an ordinary number of fittings

GAS LINE SIZING

Fig. 4

Nominal
Iron
Pipe Internal Length of Black Iron Pipe, Feet
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

Outside

Copper

Diameter, Length of Tubing, Feet
Inch

10 20 30 40 50 60 70 80 90 100

3/83926 2119

_ _____

1/29262 504137 3531292726
5/81991311079079 7267625955
3/4 329 216 181 145 131 121 112 104 95 90
7/8 501 346 277 233 198 187 164 155 146 138

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

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The water heater must be isolated from the gas supply piping
system by closing the manual shutoff valve during any
pressure testing of the gas supply piping system at test
pressures equal to or more than 0.5 psig.
The water heater, including the pressure regulator provided
with it, must not be operated at gas supply pressures in
excess of 0.5 psig. If overpressure has occurred, such as
through improper testing of the gas lines or malfunction of
the supply system, the gas valve and regulator must be
checked for safe operation. Make sure that the regulator
vent is protected against blockage.
When your connections are made, check for gas leaks at
all joints (not just the ones you made). Apply some soapy
water to all gas fittings and gas valve. Soap bubbles are a

sign of a leak.
NOTE: Do not apply soap solution to pilot filter screen or

pilot orifice area. If you have a leak, shut off the gas. After
verifying that required gaskets are in place, tighten
appropriate fittings to stop leak. Turn the gas on and check
again with a soapy solution. Never test for gas leaks using

a match or flame.

WATER CONNECTIONS

Install the heater centrally in the building if possible and
make hot water piping runs as short as possible When facing
the heater, the cold water inlet will be on the right and the
hot water outlet on the left..
Although water piping throughout the building may be other
than copper, copper or galvanized piping should be used
when connecting to the heaters ½” male NPT flex connectors
(follow local codes if more stringent). Plastics or other PEX
type plumbing line materials are not suitable for connecting
directly to the water heater. Keep water inlet pipe to no less
than ½” (19.05mm) diameter to allow the full flow capacity.
If the cold and hot connections to the heater are reversed,
the heater will not function.
The Aquastar 125BS is provided with two flexible type
connectors that must be connected to the fittings of the
water valve as shown in Fig. 6. The union end of the flexible
connectors should be attached to the rear inlet ports of the
water valve with the supplied washer gaskets. No pipe dope
or thread tape is to be used at these joints.
Be certain there are no loose particles or dirt in the piping.
Blow out or flush the lines before connecting to the water
heater. Full port valves should be installed on both the cold
water supply and hot water outlet lines to facilitate servicing
the heater (see Fig. 7). For installation on a private well
system with the use of a pressure tank, the lowest pressure
range setting recommended is 30-50 psi (2.07-3.45 bar).

Fig. 5 - Installation of Gas Pressure Regulator

The pressure regulator provided with the heater is adjusted
to deliver the proper gas pressure (as indicated on the rating
plate and in the manual for altitude up to 2000 feet (660
meters) above sea level. On appliances being installed above
2000 ft (660 meters) elevation, the inlet gas pressure should
be set at installation to the value shown below.

NOTE: The gas pressures specified below refer to
pressures taken at the test 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.

MAXIMUM INLET GAS FLOW PRESSURE SETTING

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 supplier.

GAS INLET PIPE

PRESSURE TAP

PRESSURE REGULA­TOR
(with directional arrow on
reverse side pointing
upward)

PLASTIC VENT CAP

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 Aquastar 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 Aquastar regulator. For semi­rigid 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 AQUASTAR SUPPLY ONLY, ALL
OTHER APPLIANCES IN THE BUILDING WILL NEED TO
BE INCLUDED IN THE PIPE SIZING.

National Fuel Gas Code requires that a sediment trap (drip
leg) be installed on gas appliances not so equipped. The
drip leg must be accessible and not subject to freezing
conditions. Install in accordance with the recommendations
of the serving gas supplier.
WARNING: The heater must be disconnected from the gas
supply piping system during any pressure testing of that
system at test pressures in excess of 0.5 psig.

Fig. 6 - Water valve and water connectors, top view

WASHER

WATER FILTER

WATER VALVE

WASHER

INLET

OUTLET

FLEX
CONNEC­TORS

12 6 720 606 518

OPERATING INSTRUCTIONS

Before proceeding with the operation of the heater make
sure that the system is filled with water.
Open the cold water inlet supply to the heater fully.
Open a hot water faucet to permit the water to fill the heater
and the piping and to eliminate the air trapped in the system
Close the hot water faucet after the water flows freely and
all the air has escaped from the system. The water heater
is now ready to operate.

FOR YOUR SAFETY READ BEFORE LIGHTING
THE PILOT

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 appliance has a piezo-igniter for lighting the pilot
burner. When lighting the pilot, follow these instructions
exactly.
B. BEFORE LIGHTING smell all around the appliance area
for 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 push in or turn the gas control
buttons. Never use tools. If a button will not push in, check
to make sure the buttons are being pushed in the proper
sequence. Follow these instructions exactly. If control
button(s) are jammed, close the gas supply and call a
qualified service technician. Attempted forceful repair may
result in a fire or explosion.
D. Do not use this appliance if any part has been under
water. Immediately call a qualified service technician to
inspect the appliance and to replace any part of the control
system and any gas control which has been under water.

LIGHTING INSTRUCTIONS (as seen on front cover

of heater)

1. STOP! Read the safety information above on this plate.

2. The gas valve must be turned off by depressing the gas

valve off button ( ).

3. Wait five (5) minutes to clear out any gas. If you smell
gas, STOP! Follow “B” in the safety information above
on this plate. If you don’t smell gas, go to the next step.

4. The pilot burner is located behind the peephole in the
front center of the jacket directly below this instruction
plate.

5. Depress PILOT button ( ) and light pilot by pushing
PILOT INGITER button ( ). This may have to be
repeated.

6. Observe the pilot flame through the peephole. The pilot
button ( ) should be held down at least 15 seconds with
pilot burning. When the pilot button is released the pilot
should continue to burn.

- If the gas valve button does not pop up when released,

stop and immediately call your service technician or gas
supplier.

- If pilot does not stay lit, repeat steps 1 through 6.

- If pilot will not stay lit after several tries, depress the OFF

button ( ), and call your service technician or gas supplier.

7. When lit, depress the ON button ( ). The heater will

now fire when water is drawn at a rate greater than the
threshold flow rate.

NOTE: If main burner should fail to ignite, make sure pilot
is burning. If not, repeat lighting steps 1 through 6.

TO TURN OFF GAS TO APPLIANCE

Depress the OFF button ( ) and close the gas supply to
the heater.

Connecting the pressure relief valve (PRV)

A listed pressure relief valve supplied with the heater must
be installed at the time of installation. No valve is to be
placed between the PRV and the heater. No reducing
coupling or other restriction may be installed in the discharge
line. The discharge line must be installed such that it allows
complete drainage of both the PRV and the line. The location
of the PRV must be readily accessible for servicing or
replacement, and be mounted as close to the water heater
as possible. See Fig 7. To install the PRV, a suitable fitting
connected to an extension on a “T” fitting can be sweated
to the hot water line.

Fig. 7 - Pressure Relief Valve

PIPE PRV TO
APPROPRIATE
DISCHARGE

HOT

COLD

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Fig. 8 - Characteristic Pilot Flame

3mm

Correct gap between pilot
burner tip and piezo electrode
tip

Piezo Electrode

Air screen filter

10mm

3/8”

Piezo

Electrode

Thermocouple

To clean the pilot burner and/ or the pilot orifice : Turn
off the gas at the unit. Remove the cover of the heater. To
do so, remove incandescent particle tray and unscrew the
central screw located at the bottom of the front cover. Pull
main cover out toward you and lift up and out. Pull the air
screen off, wash it and blow any lint off (See Fig 9). The
pilot orifices should also be cleaned or replaced. Do not
enlarge the orifice. Do not use any wire or sharp object to
clean orifices. Natural gas orifices are large enough that
you can usually clean them by blowing through them. LP
orifices, on the other hand, are too small to clean and should
be replaced. See #3 in Trouble Shooting Section. To access
the pilot orifice, remove 2 screws holding pilot assembly in
place. Then loosen compression fittings to expose pilot

orifice.

Fig. 9 - Pilot burner with air screen/ pilot orifice

PILOT ORIFICE

AIR SCREEN

INFORMATION ABOUT WATER TEMPERATURE

The AquaStar 125B LPS and 125B NGS water heaters
have a gas control that modulates burner output in response
to water flow. Its purpose is to ensure that the hot water
temperature will remain steady, although the water flow
demand might vary (down to 1/2 gal/minute). The AquaStar
125 B”S” will produce a temperature rise of approximately
90°F at flow rates between 0.5 and 1.8 gallons per minute
unless the water has been preheated. If the incoming water
is already hot, the burners will modulate accordingly so the
outlet temperature will not exceed 140°F.
Cold water will have to be mixed in at the faucet to produce
comfortable temperatures. Mixing in cold water will produce
higher flow rates and will reduce risk of scalding. Note: 105°
is the maximum recommended temperature for a hot bath.
Handwashing should not be done in water hotter than 112°

- and cooler for older adults, young children or persons with
sensory loss. Remember that scalding can occur in 20
seconds with 135° water.

MAINTENANCE AND SERVICE

(see maintenance table on back of manual)
Approximately once a year, the AquaStar should be checked
and cleaned. To remove the front cover, first remove the
incandescent particle tray, then unscrew the central screw
located at the bottom of the front cover. Pull main cover out
toward you and lift up and out. THE FOLLOWING
OPERATIONS SHOULD BE PERFORMED BY A
QUALIFIED SERVICE PERSON:
Vent System: Should be checked annually. Clean and repair
as needed.

Water Valve (Part # 8707002393): The water valve on
this heater should be serviced periodically. Lubricate
component #27 on page 14 with a small amount of silicon,

faucet or lithium grease every two years to keep its o rings
fresh and pushrod sliding smoothly. Every 3-5 years replace
components #27 and #29 on page 14. The frequency will
depend on the mineral content of the water and conditions
of use or whenever signs of corrosion appear at the gas and
water valve joint. Periodically check that the water inlet filter
(#34 on page 14) is clean as well.

Pilot Flame: The pilot flame should burn with a clean sharp
blue flame and should resemble the diagram in Fig 8. If the
flame is yellow, or if the pilot knob has to remain depressed
for a long time in order to keep the pilot lighted, the pilot
burner and or the pilot burner orifice may need to be cleaned
(NG), the orifice may need to be replaced(LP), and or the
air screen may need cleaning. The pilot flame should envelop
approximately 10 mm (3/8") of the tip of the thermocouple.
If it is too small, the pilot burner must be cleaned. To obtain
a spark, the position of the Piezo igniter electrode should be

approximately 3 mm (1/8") from the pilot burner tip.

Main Burner Flames: The main burner flames should be
blue, with a more intense blue cone in the center core. Yellow
flames could be a sign of wrong size gas orifices or dirty
burners, or a blockage on the heat exchangers fins.

14 6 720 606 518

If some burners have yellow flames while others have good
flames, it is likely that dust, lint or spider webs have partially
clogged the burner venturis. Contact a gas service person
to clean the remove and clean the burners.

Mineral Scale Build-up: The AquaStars heater, when
operated at lower temperatures settings, do not accumulate
mineral build-up. If however, the water has a high mineral
content, periodic descaling may be necessary. The heating
coils should be flushed with a descaling solution. Consult
your service person.

TROUBLE SHOOTING (see maintenance table)

Introduction

The AquaStar 125 B “S” 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.

Problems are stated in upper case, bold face. Most common
causes for the problems follow in order of likelihood. The
suggested solutions require that the cover be taken off. To
do this, remove incandescent particle tray and unscrew the
central screw located at the bottom of the front cover. Pull
main cover out toward you and lift up and out.

PILOT LIGHT WILL NOT LIGHT

1. No gas to the AquaStar

A. Gas cock on gas line may not be open.
B. Gas valve button has not been pushed in on “PILOT”
position ( ).
C. Gas regulator may be shut or damaged.

2. In-line AquaStar gas regulator jammed (usually on
LP gas)

Replace or unlock the regulator. Note: The regulator
furnished with the heater is designed for low gas pressure.
Excessive pressure will lock it up (propane only). Locking
usually happens if the gas pressure between the gas tank
(propane) and the water heater’s gas regulator has not been
reduced. See page 2 for recommended correct gas pressure.
To unlock a regulator, consult your gas supplier.

3. Pilot orifice clogged and/or air screen dirty, or pilot
gas filter is dirty.

Clogging of the pilot burner can be caused by dust and any
suspended matter contained in the ambient air.
Although the filters can lengthen the cleaning intervals, they
can never completely prevent such clogging. In consequence
the gas jet issuing from the pilot orifice is reduced and or
the air mixture is reduced. The pilot flame is weak and thus
can no longer heat the thermocouple sufficiently. For cleaning
purposes, the air filter screen is pulled off, washed and blown
out. The pilot orifice has likewise to be cleaned or exchanged.
Consult a gas service person to clean the pilot.

4. Air in the Gas Line
Note: Normally this is a problem only at the time of initial

installation, after the pipes have been worked on, or after a
propane tank has been allowed to empty, or after the heater
has been shut down for a long time.
Bleed all the air trapped in the gas line. Because of the very
small pilot orifice (especially on LP gas models), bleeding
out all the air could take several minutes. Depress the pilot
button ( ) and depress this button until all the air has
escaped, and the gas has arrived. During this process, press
repeatedely on the piezo ignition button until the pilot flame
has ignited.

PILOT LIGHTS BUT FLAME GOES OUT WHEN BUTTON
IS RELEASED

1. Pilot push button was not pushed in far enough or
was not held in long enough

Depress the pilot button. Hold it pushed in for at least 15
seconds to give time for the pilot flame to properly heat the
tip of the thermocouple.

2. Pilot flame improperly aimed or is too weak so it is
not properly heating the tip of the thermocouple.

The Pilot flame should be a sharp blue flame and aimed at
the tip of the thermocouple so that it envelops 10 mm (3/8
“) of the thermocouple tip. Pilot flame has to be properly
aimed at the thermocouple. See Fig 8.

3. Poor thermocouple connection at the electromagnet

Note: Electromagnet is part #8707201094 located on the

right side of the gas valve behind the piezo pushbutton
assembly. Check the tightness of the thermocouple
connection nut at the electromagnet: The Electro-magnet
connection is a large aluminum 17mm hex head nut. The
thermocouple end is a 5 mm brass nut which screws into
the 17 mm nut. Tighten the thermocouple nut snugly but not
too tight.

4. Poor circuit connections at the ECO. (Energy Cut­Off overheat protection)

Oxidation or looseness of the ECO terminal connections
can result in millivolt current loss through the thermocouple
safety circuit. Clean terminals with very fine sand paper or
an eraser and reconnect ECO leads.

5. Faulty ECO (part #8707206017)

If cleaning the terminals attached to the ECO did not fix the
problem, connect a jumper wire between the two wires and
try to relight the pilot. If the pilot flame now remains on,
replace the ECO. If the flame still goes out when the button
is released, the ECO is not defective. Go to next step.

6. Faulty thermocouple (part #8747202083) or
electromagnet) Unless these 2 parts are at least 8 to
10 years old, it is very unlikely that they are faulty.
Before testing, reconfirm that #2 is absolutely correct,
and that all connections are clean and tight.

156 720 606 518

To test the thermocouple, disconnect the thermocouple lead
to the ECO. Insert a multi-meter probe into the thermocouple
lead and attach or hold the other lead to the metal gas
valve (DC common). Light the pilot flame and hold button,
meter reading should be 24 mVDC or more. If the reading is
24 mVDC or more the thermocouple is good. To test the
electromagnet, re-connect the thermocouple lead to the
ECO, light pilot and hold button while taking a reading
between the ECO leads and the metal gas valve (DC
common). The reading should drop to 19 mVDC or less. If it
does not, replace the electromagnet.

BUR NERS DO NOT IGNITE WH EN HOT WATER IS TUR NED
ON

1. Pilot is not on.

Light the pilot. See lighting instructions.

2. Gas valve button not positioned on Burner Position

Be sure once the pilot flame is on, that after a 15 to 20
second wait, the main burner button ( ) is pushed all the
way in.

3. Cold incoming water connection made to wrong side
of heater

Make sure cold water inlet connection is on the right side of
heater when you are facing the heater.

4. Water flow rate at hot water tap is too low.

Note: The AquaStar models 125B”S” require 0.5 gallon per

minute flow to activate the burners. This is a flow which
would fill a quart jar in 30 seconds.

5. Cold water inlet filter on heater is dirty.

Remove filter and clean. This screen filter is located at the
inlet side of the brass water valve (fig. 11, #34). Check and
clean faucet aerators too.

6. Crossover in household plumbing

The AquaStar burner activates when there is sufficient water
pressure drop in the AquaStar water valve assembly — ie.
when a hot water faucet is opened. If there is a crossover in
the plumbing, the necessary pressure drop in the AquaStar
will be insufficient, or totally eliminated. A plumbing crossover
can be caused by a bad washer at a single lever faucet or
incorrect plumbing or a mixing valve in the line, etc. which
permits hot and cold water to mix in the plumbing. The
crossover will create a back pressure in the system preventing
the pressure drop in the Aquastar — i.e. cold water is entering
the water heater from both sides and the burners will not
come on. To confirm there is no crossover in the plumbing,
shut off the cold water supply to the AquaStar. Open your
hot water taps. There should not be any water flowing. If
there is water flowing, there is a crossover in the plumbing.
This is a plumbing problem, not an Aquastar problem. Please
contact your plumber.

7. Water valve parts may be dirty or components
damaged.

Water valve and component parts must be totally free of
dirt. First check that the venturi is free of dirt particles. In
hard water areas, mineral deposits can eventually (3 to 5
years in hard water areas) corrode the water valve parts to
a point where they will need replacing.

Any sign of moisture or corrosion at the joint of the water
valve and the gas valve is a sign that the water valve assembly
components need to be replaced immediately.

Note: Water valve for model 125B”S” is part # 8707002393
for both LP and NG models. (Contact service person to
clean water valve or replace if corrosion is present).

PILOT LIGHT GOES OUT DURING OR IMMEDIATELY
AFTER HOT WATER HAS BEEN USED

1. Gas pressure too low

Very low gas pressure may be caused by low delivered gas
pressure, a jammed gas regulator or undersized gas lines. If
the gas lines are undersized, there may still be the specified
static gas line pressure. However when the water valve
opens,and gas enters the burners, the pressure could drop
sharply, causing the pilot flame to go out.
Have a gas technician confirm the gas pressure both static
and at maximum Btu output. Specifications for your heater
are on page 2.

2. Pilot may be dirty or weak

See Page 13 for instructions on pilot maintenance.

3. Burners are not shutting down immediately when hot
water is turned off

Note: If burners don’t shut down immediately when the hot

water is turned off, the heater will overheat and the ECO
will shut-off the gas. Rebuild the water valve assembly using
the repair kit from BBTNA (part #8 703 406 204).

WATER IS TOO HOT

1. Water flow rate is too low.

Increase the flow rate.

2. Not enough cold water mixing at faucet

Contact your plumber to adjust mixing valves on faucets.

3. The heater’s fixed degree rise is too high for user

The calibration nut for the thermostat assembly at the gas
valve can be adjusted upward to lower the temperature rise.
A seal of paint coats two adjusting nuts there, the thin up­per one is a lock nut while the lower one is the adjuster.
Loosen the lock nut one first. Tighten the adjuster nut in­crementally upward and check water temperature, stop when
satisfactory. Then tighten down the lock nut. Caution:

Never back the adjuster nut downward to the last thread
unless the thermostat is being replaced. This is a gas

seal.

WATER IS NOT HOT ENOUGH

1. Water flow rate is too high.

Decrease the 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

16 6 720 606 518

See specifications on page 2. Unlike storage tank water
heaters, the burners of a tankless water heater must be very
powerful to heat water instantaneously since they do this
only at the time hot water is actually being used. It is therefore
imperative that the gas pressure requirement be met exactly.
Insufficient gas pressure will directly affect the water
temperature at the time of usage. See page 2 for correct
gas pressure settings.

3. Thermostat calibration is incorrect or thermostat is
defective.

Contact your service person or call BBTNA.

4. Btu input is too low due to insufficient gas supply

Make sure your main gas line is fully opened. If using LP
gas, be sure that the size of the propane tank is adequate to
supply the required gas pressure.

5. Cold water is mixing with the hot water between the
AquaStar and the outlet

Compare water temperature at outlet of the AquaStar (hold
the AquaStar’s outlet pipe with your hand) and at the tap. If
these two are very different, check for mixing valve or
plumbing crossover (see “MAIN BURNERS WILL NOT
IGNITE...” paragraph #6).

6. Parts in water valve are dirty or damaged, which will
prevent the gas valve from being fully opened.

Water valve maintenance needs to be performed, see #7
under BURNERS DO NOT IGNITE WHEN HOT WATER
IS TURNED ON.

HOT WATER TEMPERATURE FLUCTUATES / UNIT
DEACTIVATED

1. Unbalanced pressure in waterlines

The added restriction caused by the Aquastar in the hot
water system can result in uneven pressures between the
cold and the hot. In such cases when mixing cold water at
the tap, the lower hot water pressure may be overpowered
by a much higher cold water pressure, which may cause the
Aquastar burners to shut down (deactivate). Make sure faucet
aerators or shower heads are free of minerals.

Do not add any flow restrictor to the shower head.

Typically this deactivation symptom is a result of the hot
water being too hot to use comfortably. Warm inlet water
generally causes this. Lowering the control knob setting
and/or reducing the inlet gas supply to the heater should
correct this deactivation symptom.

2. Inlet water pressure is erratic due to inadequate supply
water pressure or saturated pressure tank on well
system

For installation on a private well system with the use of a
pressure tank, the lowest pressure range setting
recommended is 30-50 psi (2.07-3.45 bar). Confirm that
the pressure tank is not water logged.

3. Cold water is mixing with the hot water between the
AquaStar and the outlet

See #6 under “MAIN BURNERS DO NOT IGNITE WHEN
HOT WATER TURNED ON”.

4 . Insufficient gas pressure

Note required gas pressures (page 2) and consult gas service
person.

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1. Heat exchanger

2. Pilot assembly

3. Burner manifold gas
pressure test nipple

4. Main gas burner

5. Pilot gas tubing

6. Gas valve

7. Piezo igniter

8. Location of pressure tap
screw

9. Water valve

10. Gas inlet gas pressure
test nipple

5

1

4

7

9

3

10

6

2

8

Fig. 10 - Diagram of AquaStar 125 BS

18 6 720 606 518

AQ 125 BS

Fig. 11 - INTERIOR COMPONENTS DIAGRAM AND PARTS LIST

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Fig. 11

INTERIOR COMPONENTS DIAGRAM

AND PARTS LIST 125BS

1 Cover 8 705 421 033
2 Cap cover 8 703 304 011
3 Water connection gasket 8 710 103 043
4 Draft divertor 8 705 505 354
5 Heat exchanger 8 705 406 189
6 Hot water pipe 8 700 705 431
7 Cold water pipe 8 700 705 294
8 Heat exchanger washer 8 710 103 045
9 Overheat sensor (ECO) 8 707 206 017

10 Main burner assembly 8 708 120 296 LP

Main burner assembly 8 708 120 298 NG

11 Pilot burner assembly 8 718 105 051

11a Pilot filter screen 8 700 507 055

12 Piezo electrode 8 708 107 002
13 Pilot orifice 8 708 200 005 NG

Pilot orifice 8 748 200 173 LP

14 Pilot Tube 8 710 707 166
15

Thermocouple 8 747 202 083

16 Burner assembly washer 8 710 103 060
17 Gas valve 8 707 011 467 LP

Gas valve 8 707 011 469 NG

18 Gas supply pipe 8 700 705 464
19 Electromagnet 8 747 201 094
20 Electromagnet washer 8 700 103 144
21 Gas filter 8 700 507 051
22 Thermocable 8 747 202 078
23 Thermostat 8 707 206 039
24 O ring Thermostat 8 700 205 101
25 O ring Thermostat 8 700 205 041
26 Water valve assembly 8 707 002 393
27 Pushrod 8 703 406 204
28 Water valve diaphragm 8 700 503 050
29 Slow ignition valve 8 708 503 062
30 Water valve setting screw 8 703 404 092
31 O ring setting screw 8 700 205 050
32 Water valve venturi 8 708 205 235
33

Water valve piston assembly 8 708 500 230

34 Water inlet filter 8 700 507 059
35 Water elbow fitting 8 700 703 114
36 Water valve set screw 8 703 401 051

20 6 720 606 518

Fig. 12 - Flow chart of Aquastar 125 BS

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LIMITED WARRANTY

Aquastar

General

Aquastar water heaters are warranted by the Manufacturer
(BOSCH) through BBT North America. BBT North America
(BBTNA) will furnish a replacement heat exchanger and will
furnish a replacement of any other part which fails in normal
use and service within the applicable periods specified
below, in accordance with the terms of this warranty. The
BBTNA replacement will be warranted for the unexpired
portion of the original warranty. This warranty will be valid
only for water heaters in possession of the original purchaser
as recorded on the warranty card.

The heat exchanger

If the heat exchanger fails within twelve (12) years after the
original installation and operation BBTA will furnish a
replacement heat exchanger. However, if the water heater
is installed in other than a single family dwelling this heat
exchanger warranty is limited to two (2) years from date of
original installation and operation.

Exceptions

This warranty will not apply:

1. to defects or malfunctions resulting from failure to properly

install, operate or maintain the unit in accordance with
the printed instructions provided;

2. to damage or abuse, accident, neglect or freezing and

other acts of nature;

3. to damage resulting from operation with either the flame

sensor rod or overheat sensor removed;

4. to failure of the heat exchanger resulting from the

operation of the water heater in a corrosive atmosphere
or at water temperatures exceeding the maximum rating,
or if the water heater is not supplied with potable water;

5. to defects or damage cause by any attachment

or modification, including any energy-saving device.

All other parts

If any other part fails within two (2) years after original
installation and operation, BBTNA will furnish a replacement
part free of charge.

Shipping costs

In addition to supplying the replacement part(s), BBTNA
will provide ground service delivery for these parts. Expedited
or upgraded shipping will be charged to the customer.

Service labor costs

This warranty does not cover any labor costs associated
with service, removal or re-installation of part(s). All such
costs must be borne by the Purchaser. Additionally, this
warranty does not cover any labor costs associated with
service, removal or re-installation of the original water heater
or a replaced water heater.

How to Make a Claim

Any claim for warranty parts should be made to your local
dealer, distributor or to BTNA. If BBTNA, please contact the
Technical Support Department:

BBT NORTH AMERICA
340 Mad River Park
Waitsfield, VT 05673
Phone: [phone]
www.boschhotwater.com

In most cases, the dealer or distributor will be able to promptly
honor your claim and subsequently notify BBTNA. However,
all replacements are made subject to validation by BBTNA
of in-warranty coverage. The damaged or defective item must
be made available in exchange for the replacement.

Miscellaneous

No one is authorized to make any other warranties on behalf
of BBTNA. It is expressly understood that the replacement
warranty of BBTNA shall be in lieu of any and all other
warranties, express or implied, including warranties of
merchantability or fitness for a particular use or purpose,
and further that BBTNA shall not be liable for any loss or
damage directly or indirectly arising from the use of the hot
water heater, or for any consequential damages arising from
such use (including damages from water leakage). BBTNA’s
sole liability with respect to any defect shall be for the
replacement of the defective part(s). Some states do not
allow such limitations and exclusions, so the above may not
apply to you.
This warranty gives specific legal rights. You may also have
other rights which vary from state to state.

22 6 720 606 518

236 720 606 518

Replacement Parts available:

BBT NORTH AMERICA

Bosch Group

Bosch Water heating
340 Mad River Park
Waitsfield, Vermont 05673
Phone [phone]
Fax [phone]
www.boschhotwater.com
[e-mail]

VULCANO T ermodomésticos S.A.

Estrada de Cacia

3801 - 856 Aveiro - PORTUGAL

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© 2006 BBT NORTH AMERICA,
Waitsfield, VT all rights reserved